Chemistry 9th Chap 14 : Topic 2 - Maryam Publications

Chemistry Chapter 14 : Topic 2

Chemical Properties of Alkanes

1 / 20

Which statement best explains why alkanes are generally considered unreactive under normal conditions?

A) They consist of only single covalent (sigma) bonds which are relatively stable and non-polar.

B) They have strong ionic bonds between carbon and hydrogen atoms.

C) They readily gain electrons due to high electronegativity difference.

D) They contain double bonds that easily break and react.

2 / 20

Although alkanes are generally unreactive, they still undergo combustion. Which explanation best justifies this exception?

A) Alkanes decompose spontaneously without oxygen.

B) Oxygen reacts with alkanes under suitable conditions producing energy.

C) Alkanes contain chlorine which supports combustion.

D) Combustion requires breaking ionic bonds in alkanes.

3 / 20

Which condition is essential for substitution reaction of methane with chlorine?

A) Presence of catalyst like iron

B) Electric current

C) UV light or sunlight

D) High pressure and water

4 / 20

In the substitution reaction of alkanes with chlorine, what is the main product formed?

A) Carbon dioxide and water

B) Alkene and hydrogen gas

C) Alcohol and water

D) Chloroalkane and hydrogen chloride

5 / 20

Why do alkanes not react easily with acids, bases, or oxidizing agents under normal conditions?

A) They lack functional groups and have stable non-polar covalent bonds.

B) They are ionic compounds.

C) They contain free electrons.

D) They have strong polar bonds.

6 / 20

Which statement correctly describes complete combustion of alkanes?

A) It produces carbon and hydrogen gas.

B) It produces carbon monoxide and water.

C) It produces carbon dioxide and water with energy release.

D) It produces chlorine and hydrogen chloride.

7 / 20

What is observed during incomplete combustion of alkanes?

A) No flame is produced

B) Formation of carbon monoxide and soot

C) Formation of only carbon dioxide

D) Blue flame with maximum energy

8 / 20

Which property of alkanes makes them suitable as fuels despite being chemically unreactive?

A) They are toxic and highly reactive.

B) They are insoluble in water and non-reactive but release large energy on combustion.

C) They form ionic compounds easily.

D) They easily polymerize at room temperature.

9 / 20

During chlorination of methane, why is the reaction described as a substitution reaction?

A) Hydrogen atom is replaced by chlorine atom.

B) Methane breaks into smaller molecules.

C) Carbon atom is replaced by chlorine atom.

D) Chlorine is added without removing any atom.

10 / 20

Which feature of alkanes mainly contributes to their low chemical reactivity?

A) Saturated structure with single bonds only

B) High polarity of molecules

C) Presence of double bonds

D) Presence of triple bonds

11 / 20

What happens when methane reacts with chlorine in the presence of sunlight for a long time?

A) Methane turns into ethene.

B) Only one product is formed.

C) No reaction occurs.

D) Multiple substitution products can form.

12 / 20

Which statement best compares alkanes with alkenes regarding reactivity?

A) Alkenes are less reactive due to saturation.

B) Alkanes are less reactive due to lack of double bonds.

C) Alkanes are more reactive due to double bonds.

D) Both are equally reactive in all conditions.

13 / 20

Why does combustion of alkanes release energy?

A) Chlorine atoms release energy during reaction.

B) Energy is released when new stronger bonds form in CO₂ and H₂O.

C) Energy is absorbed to form bonds in products.

D) Alkanes contain stored electrical energy.

14 / 20

Which observation indicates that combustion of an alkane is incomplete?

A) Formation of chlorine gas

B) No flame at all

C) Yellow smoky flame with soot deposition

D) Clean blue flame and no smoke

15 / 20

Why are alkanes considered saturated hydrocarbons?

A) They contain double bonds.

B) They contain maximum possible hydrogen atoms bonded to carbon.

C) They contain oxygen atoms in structure.

D) They are soluble in water.

16 / 20

Which condition is NOT required for combustion of alkanes?

A) Oxygen

B) UV light

C) Fuel (alkane itself)

D) Heat or ignition source

17 / 20

In chlorination of alkanes, what initiates the reaction mechanism?

A) Breaking of carbon-carbon double bonds

B) Formation of hydrogen gas first

C) Formation of ions in water

D) Homolytic cleavage of Cl₂ producing free radicals

18 / 20

Which property explains why alkanes do not decolorize bromine water under normal conditions?

A) They are acidic in nature.

B) They are saturated and do not undergo addition reactions easily.

C) They are ionic compounds.

D) They contain oxygen.

19 / 20

What is the main environmental concern associated with incomplete combustion of alkanes?

A) Increase in nitrogen concentration

B) Production of oxygen gas

C) Formation of water vapor only

D) Release of carbon monoxide, a poisonous gas

20 / 20

Which statement best summarizes the chemical behavior of alkanes?

A) Highly reactive due to unsaturation

B) React vigorously with water

C) Always form ionic compounds

D) Generally unreactive but undergo combustion and substitution under specific conditions

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