LEARNING HUB.TZ

CHEMISTRY EXAMINATION FORM THREE

TOPICAL EXAMINATIONS.

NON-METALS

NAME………………………………………..CLASS…………………………………………….……………TIME: 2¹/₂HRS

INSTRUCTIONS:-

1. This paper consists of sections A, B and C

2. Answer all questions

3. All answers must be written in the spaces provided

4. All writings should be in blue/black inks except for drawings that should be in pencils

5. The method of collecting hydrogen chloride gas in a class experiment is known as:

1. Downward displacement of water

2. Downward displacement of air

3. Upward displacement of air

4. Fountain

5. Condensation

6. Which action should be taken immediately after concentrated sulphuric acid is spilled on the skin?

1. It should be rinsed off with large quantities of running water.

2. It should be neutralized with solid CaCO₃.

3. It should be neutralized with concentrated NaOH.

4. The affected area should be wrapped tightly and shown to medical health provider.

5. It should be neutralized with concentrated KOH.

7. The only metal which does not react with dilute hydrochloric acid is:-

1. Magnesium

2. Aluminium

3. Copper

4. Zinc

5. Sodium

4. Which among the following equations correctly shows the reaction between chlorine gas and water?

1. C l_2(g) + H₂0₍₁₎ → CI_2(g)

B 2C1_2(g) + 2H₂0₍₁₎ → 4C1^-1_(aq) + 0_2(g) + 2H_2(s)

3. Cl_2(g) + H₂0₍₁₎ →HCl + HOCI(aq)

4. 2Cl_2(g) + 2H₂0(_I) →2H0C1 +H_2(g)

5. 2C12(g) + 3H₂0₀₎ → C1_{2 (.0} + 2H₃0⁺

(v) Which of the following pair of gas can be prepared in the laboratory an: collected over water?

1. Oxygen and Ammonia

2. Hydrogen and Hydrochloric acid

3. Hydrogen and Oxygen

4. Oxygen and Hydrogen chloride

5. Hydrogen and Ammonia

(vi) Two substances are allotropes of carbon if they:

A. both reduce heated iron (III) oxide to iron

B. have different crystalline structure

D. have equal masses

C. have equal shape

E. have the same arrangement of atoms

vii) Which of the following sets of elements is arranged in order of increas­ing electro negativity?

A. Chlorine, fluorine, nitrogen, oxygen, carbon

B. Fluorine, chlorine, oxygen, nitrogen, carbon

3. Carbon, nitrogen, oxygen, chlorine, fluorine

4. Nitrogen, oxygen, carbon, fluorine, chlorine

5. Fluorine, nitrogen, oxygen, chlorine, carbon

viii) The gas formed when dilute nitric acid reacts with magnesium metal is;

1. Nitrogen

2. Hydrogen

3. Oxygen

4. Nitrogen dioxide

ix) Which of the following is true about carbon?

1. Carbon dioxide is very acidic

2. Solid carbon d

2. Match the items in list A with the responses in list B by writing the letter of the correct response beside the item number.

3.(a) With the help of chemical equation, what will be observed when ammonia reacts with:

1. Hydrogen chloride?

2. Copper (II) oxide?

(b) It is not advisable to sleep inside a house which is not well ventilated with a burning wooden charcoal. Give a reason for that and write the chemical equation to represent your answer.

4 .(a) The chemical properties of concentrated sulphuric acid can be grouped into oxidizing property and dehydrating property. In which property should sulphuric acid be grouped when it reacts with copper metal? Give reason and write the equation of the reaction.

(b)The preparation of chlorine gas can be represented by the following equation:

Mn0₂ + 4HCI→ MnCl₂ + 2H₂0 + Cl₂.

Calculate the number of moles of HCI which are needed to react with 20g of Mn0₂ and list two main chemical properties of chlorine gas.

5. (a) (i) What is the name given to the different forms of the element which exists in the same physical state?

(ii) Carbon exists in two different forms of the same physical state and one of those carbon forms is represented by structure X below. Give the name of the carbon form with structure X.

3. Name the second form of carbon.

4. State one property and one use which depends on the property you have stated for each form of carbon.

5. Carbon can be used to convert copper II oxide to copper as shown in the equation.

C_(S) + 2CuO_(s) → 2Cu_cs) +CO_2(g)

What is the function of carbon in this equation?

1. Calculate the mass of CuO which can react with 12g of carbon in the equation given in 5 (b) (i) above.

2. What is the effect of carbon monoxide in the blood?

7.(a) Identify the substances by using the following information:

1. A solid is yellow when hot and white when cold.

2. When water is added to a white powder heat is evolved and the white powder changes to blue crystals.

3. An aqueous solution of a greenish crystalline sulphate forms a pale-green precipitate with sodium hydroxide solution which turns to brown on standing and when exposed to air.

4. A colourless gas turns a yellow acidified potassium dichromate paper to green.

5. A colourless gas becomes brown on exposure to air.

(b) With the help of chemical equations explain what happens to the following compounds of ammonia when heated in separate test tubes:

1. A mixture of ammonia chloride and sodium hydroxide solution

2. Ammonium chloride crystals

3. Ammonium nitrate crystals

4. Ammonium sulphate crystals

5. Ammonium nitrite crystals

8. The Diagram below shows the preparation of chlorine gas in a laboratory fume-chamber. Study the diagram and answer the questions that follow.

(a) What do letters A, 8, C, D and E represent?

1. Why is the gas prepared in the fume-chamber?

2. Can the gas be collected over water? Why?

3. What will happen to a damp blue litmus paper if it is introduced into a gas jar full of chlorine gas?

4. What will happen if a gas jar of hydrogen sulphide is inverted over a gas jar of chlorine such that the two gases get mixed? Write a balanced equation for the reaction which will take place between hydrogen sulphide gas and chlorine gas.

(b) (i) List down two uses of chlorine gas.

(ii) Give a balanced chemical equation for the method of preparation of chlorine used in this question.

9. (a) Write ionic equations for the following:

1. Laboratory preparation of ammonia gas.

2. Precipitation of barium sulphate from barium chloride and sodium sulphate and silver chloride from a soluble chloride.

3. Neutralization of a strong acid and a strong alkali.

(b) Consider the following elements of group seven in the order in which they appear in their group in the Periodic Table. F, C, Br, and I.

1. Which element is the most electronegative?

2. Name the least electronegative element.

3. Which element has the largest atom?

4. Write the electronic configuration of the chlorine atom.

(c) Define electro-negativity

11. Which method is used in the laboratory gas preparation of:

1. Ammonia?

2. Chlorine?

3. Hydrogen?

Give reasons for your answers.

(c) What will happen when:

1. yellow flowers are introduced into a gas containing chlorine gas?

2. a burning splint is introduced into a gas jar containing hydrogen gas?

3. a glass rod which was dipped in concentrated hydrochloric acid is introduced into a gas jar containing ammonia gas?

4. sulphur dioxide gas is bubbled through a yellow acidified potassium dichromate solution?

12. The preparation of ammonia in the laboratory is done by heating a mixture of ammonium chloride and sodium hydroxide.

(a) (i) Write a balanced chemical equation for the above reaction.

(ii) Using balanced chemical equations, state how ammonia reacts with hydrogen chloride gas and heated copper (II) oxide.

(b) (1) State two uses of ammonia.

(ii) Name the catalyst used in the preparation of ammonia.

(c) Explain each of the following reactions, giving observations and equations.

1. Aqueous ammonia is added to iron (III) chloride, little by little, until in excess.

2. Sodium nitrate is strongly heated.

LEARNING HUB.TZ

CHEMISTRY EXAMINATION FORM FOUR

TOPICAL EXAMINATIONS.

ORGANIC CHEMISTRY

NAME………………………………………..CLASS…………………………………………….……………TIME: 2¹/₂HRS

INSTRUCTIONS:-

1. This paper consists of sections A, B and C

2. Answer all questions

3. All answers must be written in the spaces provided

4. All writings should be in blue/black inks except for drawings that should be in pencils

SECTION A 20 MARKS.

1. MULTIPLE CHOICE QUESTIONS.

1. The empirical formula of a certain compound is CH₃. Its molar mass is 30g. What will be its molecular formular?

A. CH ₄ B. C₇ H ₄ C. C₃ H ₆

D. C₂H₈ E. C₄H₁₂

ii) C₂H₄C1 can be represented in different structures which are called:

1. Homologous series

2. Isomers

3. Structural formular

4. Identical structures

5. Condensed structures

(iii) When an alcohol reacts with a carboxylic acid they form an organic compound called:

A. an alkyne B. an ester

C. a haloalkane D. an alkene

E. an alkane

(vi) The compound CH₃CH₂CI is named as:

1. carbon dichloride

2. methyl chloride

3. methyl chloride

4. ethyl chloride

5. propyl chloride

(v) A gas burned in air forms carbon dioxide and water only. From this experiment the gas is likely to be:

1. Hydrogen

2. Carbon dioxide

3. Ethane

4. Nitrogen

5. Ozone

(vi) The correct chemical equation for the combustion of ethanol is:

1. CH,CH₂OH +1/20₂ →CH₃CH0+ H₂0

2. CH₃CH₂OH + 30₂ → C0₂ +3H₂0

3. CH,CH₂OH + 0₂ → CH,COOH + H₂O

4. CH,CH₂OH + 20₂ → 2C0 + 3H₂0

5. CH₃CH₂OH + 20₂ → HCO + CO₂ + H₂O + H₂

7. When ethane (c₂H₆ ) burns in air with a bright smoky flame, the product(s) formed will be:

1. carbon dioxide gas

2. carbon dioxide gas and water

3. water

4. water and oxygen gas

5. oxygen gas

(viii) Which group of organic compounds is prepared by the dehydration of the corresponding alcohol?

1. Alkynes

2. Alkenes

3. Alkanes

4. Esters

5. Carboxylic acids

(ix) Alkynes are organic compounds whose homologous series has a general molecular formula of:

1. C_nH_2n

2. CH_(2n+2)

3. C_nH_(2n-2)

4. C_nH_(2n+1)

5. C_nH_(n+2)

(x) An organic compound of structural formula R-COOH belongs to the homologous series of:

1. alkenes

2. esters

3. alcohols

4. alkanes

5. acids

2. MATCHINGITEMS QUESTIONS

LIST A

LIST B

Have the same general formula Break down of large alkane into smaller alkane. Same molecular formular but different structural formula Reaction that mostly occurs in alkanes Has double bond or triple bond Self addition of alkanes to form a larger molecule Sweet smelling substance Process by which alcohol is formed in laboratory The product formed when ethene is hydrated using phosphorus catalyst Substance that increases the cleaning ability of water.

Soap Detergent Esterification Ester Substitution reaction Chain reaction Elimination reaction Hydrolysis Polymerization Saturated hydrocarbon Unsaturated hydrocarbon Polymer Homologous series Isomers Isomerism Cracking Fractional distillation Fermentation Alcohol Carboxylic acid

SECTION B.

3. Consider a four carbon hydrocarbon (C₄Hn), where n is an integer. Give the name of homologous series, molecular formula and structural formula for different isomers of the compound formed by each homologous. In each case indicate the causes of isomerism.

4. a) (i) Define isomerism.

(ii) Write down the molecular structure and IUPAC names of the isomers whose molecular formula is C₄H_10.

b) Name the homologous series of organic compounds which are represented by the molecular formulae:

C_nH(2n+2)

C_nH2n

CnH(2n+2)O(In each case n =1,2,3...)

(c) Complete the following equations of chemical reactions and give the IUPAC names of each organic compound which appears in each equation:

1. CH4 + 0₂→

2. C₂H4, + Cl₂→

3. CaC₂ + 2H₂O →?

5. (a) Chemical analysis shows that the empirical formula of a compound is CH₂O and its relative molar mass is 60.

1. Calculate its molecular formula.

2. Name the compound formed and write its open structural formula.

(b) Write balanced chemical equations of the reaction between the compound named in 8(a) (ii) above and:

1. Sodium metal

2. Ethanol

3. Sodium hydroxide

6. State the common names of the chemical reactions represented by the equations in 8(b) (ii) and 8(b) (iii) above.

(a) Define the following terms:

1. Homologous series

2. Isomerism

(b) Write down the expanded structural formulae of the following compounds:

1. Chloroethane

2. 2-methylbutane

3. Ethanol

4. 2, 2-Dimethylpropane

(c) Complete the following reactions:

(i) CH₂ = CH, + 0₂ →? (ii) CaC₂+2H₂0 →?

(iii) CH4 +C1_{2 }? (iv) C₂ H₅0H + 0₂ →?

6. (a) Define the following:

1. A homologous series

2. Hydrocarbons

3. Isomerism

2. Write the structural formulae of all possible isomers of hydrocarbons whose molecular formula is C₄H₁₀ and give their IUPAC names.

3. You are provided with the following compounds:

H H H H H H

1. H─C─C─H B. H─ C═C─H C. H─C─C─OH

H H H H

1. H ─C≡C─H

1. Give the systematic IUPAC names of the compounds A, B, C and D.

2. How can you distinguish compound A from D?

8. (a) Classify the following compounds as alkanes, alkanes and alkynes C₇H₁₂ ,C₄H₁₀ ,C₅H₅„ C₃H₄ ,C₂H₄ and C₆H₁₂

(b) Complete and balance the following chemical equations:

1. CH ═ CH + 0₂ →

2. CH,CH₂OH + Na →

3. CH₃C00H+ KOH →

4. CH₂ ═CH₂ + CI₂

(c) Write down the condensed structural isomers of alcohols of moleculer ^­formula C₄H₉OH.

9. (a) Which homologous series of organic compounds can be represented by the following general formula?

(i) C₆H2n +2 (ii) CnH2n (iii) CnH2+1OH

2. Give the name of the first compound in each series.

3. (i) Describe a reaction by which a named compound of series in (a) (ii) can be converted to a compound of series in (a) (i).

(ii) How can a compound of series (a) (iii) be converted to a compound of series in (a) (ii)?

10. (a) (i) State three characteristics of a homologous series.

2. Draw the displayed/open structure formula of 2, 2-dichlorohexar:-:

3. Giving two reasons, explain why 2, 2-dichloro-3-methylbutane has structural isomer of 2,2-dichloropentane.

11. The following are the general structural formulae of certain organic compounds: R-OH, R-COOH, and RCOOR.

(a) Name the:

1. Homologous series represented by

R - OH, R - COOH and R - COOR and RCOOR.

2. Functional groups represented by R-OH and R-COOH.

(b)Write down the chemical equation of the reactions between the following:

1. Ethanol and sodium metal.

2. Propanol warmed with excess acidified potassium permanganate.

3. Propanol and acetic acid warmed together in the presence of concentrated sulphuric acid.

12. (a) Write the formula for the following compounds:

(i) But-2-ene

(ii) Pent-2-yne

(iii) 1, 2 dichloroethane

(iv) 2, 4 dimethylhexane

(b) Briefly explain what will be observed when silver nitrate solution is added to aqueous solution of sodium chloride.

LEARNING HUB.TZ

CHEMISTRY EXAMINATION FORM FOUR

TOPICAL EXAMINATIONS.

POLLUTION

NAME………………………………………..CLASS…………………………………………….……………TIME: 2¹/₂HRS

INSTRUCTIONS:-

1. This paper consists of sections A, and B

2. Answer all questions

3. All answers must be written in the spaces provided

4. All writings should be in blue/black inks except for drawings that should be in pencils

SECTION A 20 MARKS.

1. The problem of acid rains is now a reality in industrialized countries. The gases which escape from industries into the atmosphere and cause acid rains include:

1. nitrogen, carbon dioxide and chlorine

2. chlorine, nitrogen monoxide and ammonia

3. chlorine, carbon dioxide and sulphur dioxide

4. nitrogen dioxide, carbon dioxide and sulphur dioxide

5. chlorine, nitrogen and nitrogen monoxide

2. Which of the following actions would result into an increase in the temperature of the earth?

1. Increase of distance from the sun

2. Removal of water vapour from the atmosphere

3. Increase of cloud cover

4. Removal of noble gases from the atmosphere

5. Increase of the carbon dioxide content of the atmosphere.

3. which of the following is not a type of pollution?

1. Aerial pollution

2. Marinepollution

3. Water pollution

4. Terrestrial pollution

4. which of the following is not a typeof land pollution?

1. Nuclear waste

2. Homegarbage

3. Fertilizers

4. Solid chemicalwastes

v) which of the following ispoint source of water pollution?

A. Fertilizer from the farm

B. Oil spills

C.Liquid industrial effluent

D. Release of sewage waste into water bodies

vi) excessive growth of water plants and algae is called?

1. Point pollution

2. Leaching

3. Eutrophication

4. Dead zones

vii) the majorcomponent of photochemical smog is;

1. Ozone

2. Particulate matter

3. Carbon monoxide

4. Nitrogen dioxide

viii) which of the following chemical does not contribute to global warming?

1. H2

2. CH4

3. CO2

4. N2O

IX) The zone of the atmospherewhich contains the ozone layer is called?

1. Mesosphere

2. Stratosphere

3. Higher atmosphere

4. Troposphere

x) the compound of sulphur that causes acidic rain is;

A. Sulphur dioxide

B. Sulphur trioxide

C. Hydrogen Sulphide

D. Sulphuric acid

2. Matching items Questions.

SECTION B.

3. (a) Define the following terms:

(i) Pollution

(ii) Pollutant

2. List down the three main types of pollution.

3. (i) Define "green house effect".

(ii) Why does the increase of the concentration of carbon dioxide gas in the atmosphere result into increase of the earths surface temperature?

(iii) What is the function of ozone layer at the top of earths atmosphere?

(iv) List down any two gases produced by industries that destroy the ozone layer.

4. (a) (i) Define the term pollution.

(ii) List down the three (3) main types of pollution.

(ii) What is the importance of ozone layer in the earths atmosphere?

1. Explain the effect of destroying the ozone layer.

© Which gases must not be produced in order to prevent the destruction of ozone layer?

5. (a) (i) Define the term terrestrial pollution.

(ii) Mention three (3) materials that contribute to terrestrial pollution.

(iii) Mention three (3) gases which cause acid rains.

(b) Explain the effect of the following to the environment:

1. Acid rain

2. Artificial fertilizer

3. Plastic containers

6. (a) (i) Define the term fertilizer.

(ii) What are the three (3) effects of excessive nitrogen to plants?

(b)(i) State four (4) methods of application of fertilizers.

2. What are the four (4) advantages of using manures in the farms?

3. Calculate the percentage composition of nitrogen in ammonium sulphate fertilizer (NH₄ )₂ SO₄ .

6. (a) (i) What does the term terrestrial pollution mean?

2. Mention three (3) causes of terrestrial pollution.

3. Explain four (4) methods of preventing terrestrial pollution.

(b) What is the effect of ultraviolet radiations on living organisms?

(c) (i) What is the function of ozone layer in the atmosphere?

(ii) What control measures should be taken to prevent the destruction of ozone layer?

8. (a) Mention three (3) natural resources that should be protected from pollution.

(b) Name two (2) pollutants in each of the following:

1. Land

2. Water

3. Air

(c) (i) Explain the effect of carbon monoxide to the human body.

(ii) Give three (3) examples of gases which cause greenhouse effect.

9.Describe five causes and effects of soil pollution.

10. a) what is ozone layer?

b) name four ozone layer depleting substances

c) suggest two things that should be done to prevent ozone layer from depletion

11. Eutrophication is the excessive growth of aquatic plants and algae in water bodies

b) Give two causes of eutrophication

b) Explain three effects of eutrophication

c) Explain four ways in which mining contribute to water pollution.

LEARNING HUB.TZ

CHEMISTRY EXAMINATION FORM THREE

TOPICAL EXAMINATIONS.

SOIL CHEMISTRY.

NAME………………………………………..CLASS…………………………………………….……………TIME: 2¹/₂HRS

INSTRUCTIONS:-

1. This paper consists of sections A, B and C

2. Answer all questions

3. All answers must be written in the spaces provided

4. All writings should be in blue/black inks except for drawings that should be in pencils

SECTION A 20 MARKS.

1. Addition of sulphate of ammonia to the soil corrects the deficiency of:

1. oxygen and nitrogen

2. nitrogen and hydrogen

3. nitrogen and sulphur

4. sulphur and oxygen

5. sulphur and hydrogen

2. a straight fertilizer contains

1. Two primary micronutrients

2. Only one primary macronutrient

3. One primary macronutrient and one micronutrient

4. Two macronutrients

3. Which of the following best describes a manure?

1. Organic substances of animal and plants origin

2. Are plants wastes

3. A mixture of different fertilizers

4. Products of parent rock disintegration

4. Which of the following compounds can be suitable for liming?

1. Calcium oxide and hydroxide

2. Magnesium oxide and sodium hydroxide

3. Calcium oxide and sodium hydroxide

4. Magnesium hydroxide and sodium oxide

5. Which of the following explain weathering?

1. Breakdown of soil particles to facilitate erosion

2. Break down of parent rock to facilitate erosion

3. Break down of organic matter in the process of soil formation

4. Break down of synthetic fertilizer to facilitate to enhance absorption

6. Which of the following is not a cause of loss of soil nutrients?

1. Liming

2. Leaching

3. Soil capping

4. Soil erosion

7. The following are factors affecting soil PH except One, which one?

1. Parent rock

2. Fertilizers

3. Human activity

4. Rainfall

5. Non of the above

8. Which of the following is not a straight fertilizer?

1. Ammonium fertilizers

2. Phosphate fertilizer

3. Potassic fertilizer

4. Nitrogenous fertilizer

9. Which of the following does not facilitate chemical weathering?

1. Hydrolysis

2. Dissolution

3. Oxidation

4. Soil reaction

10. The process by which soluble nutrients are washed into the lower layers of the soil and beyond the roots is called

1. Soil reaction

2. Soil erosion

3. Leaching

4. Leachate

2. Matching items questions.

3. (a) Give the meaning of the following terms:

1. Soil pH

2. Liming

3. Macronutrient

2. (i) Define soil erosion.

(ii) List down four main causes of soil erosion.

4. A) List down four advantages of organic manure over artificial fertilizers.

2. (i) What is meant by the term "nitrogen fixation"?

(ii) State two major processes by which the atmospheric nitrogen is converted to usable form in the soil.

4. (a) What do you understand by each of the following?

1. Soil reaction

2. Liming

b) (i) Differentiate active acidity from potential acidity. (ii) What is a fertile soil?

(iii) State four (4) factors that affect soil fertility.

(c) (1) Name four (4) nitrogenous fertilizers.

2. What is manure?

3. Name four (4) types of organic manure.

4. (a) What do you understand by the following terms?

1. Soil erosion

2. Leaching

3. Soil fertility

4. Soil pH

2. The weight of fresh soil collected from a farmers field was 24g. It was oven-dried at 106°C for 22 hours, cooled in a desiccator and weighed. The oven-dry weight was 19.5g. What was the percentage of moisture in the soil sample?

c) Explain why a good farmer is advised to include leguminous plants in crop rotation.

7. a) Group the following plant nutrients into macro-nutrients and micro-nutrients: S, Zn, Mo, N, Cl, P, Co, K and Ca.

b) Give one function of each of the following essential plant nutrients:

(i) N (ii) P (iii) Zn

c) A certain soil requires 40kg of nitrogen per litre in order to fulfill the plant requirement of nitrogen. Calculate in kg the quantity of ammonium sulphate {(NH4 )₂ SO₄} fertilizer required to meet the demand.

8. (a) Define the following terms:

1. Soil

2. Soil profile

3. Micronutrients

2. Explain why a fertile soil is not necessarily productive.

3. Soil erosion is one of the problems facing many farming areas in Tanzania leading to poor harvest. As a chemist give four advices to the farmers to overcome soil erosion.

9. (a) Briefly explain each of the following:

(i) Soil pH (ii) Basic soil (iii) Terracing

(b) The weight of a fresh soil sample from a school farm was 55gm. The sample was dried in an oven at 200°C, cooled in desiccators and re-weighed. The weight of the sample, after cooling to constant weight was 46gm. What was the percentage of water in the soil sample?

(c) (i) List at least two chemical substances used to neutralize soil acid.

(ii) Why do we classify nitrogen as a macronutrient in regard to plants nutrients?

10. (a) (i) What are the natural causes of soil acidity?

(ii) What cations prevail in acidic soils?

(b) (i) On treatment with calcium hydroxide the soil pH was raised from E to 7. What can you say about the properties of calcium hydroxide^-

2. What effects can the alkalinity of a soil have on the availability c: nutrients?

3. Is it sensible to add lime to a field which has received an application of ammonium sulphate fertilizer? Explain.

(c) With reference to pH, solubility and any other factors, list the ma]:: properties of the following fertilizers used in our country:

1. Ammonium sulphate

2. Super phosphate

3. Urea

(d)Give the meaning of the following terms:

1. Soil structure

2. Acidic soil

3. Liming

11. Addition of inorganic fertilization in the farm is not as important as addition of organic manure. Discuss the correctness of this statement in four points.