Chemistry Class 10 Chapter 12 Important MCQs Federal Board

Class 10 Chemistry

Hydrocarbons Important mcqs

Multiple Choice Questions:

1. Hydrocarbons are

1. Only carbon-containing compounds
2. C and H containing compounds
3. C, H and at least one electronegative atom containing compounds
4. None of them

Solution:

• Organic compounds, having only C and H atoms are called hydrocarbons.
• Therefore the answer is (C and H containing compounds)

2. Hydrocarbons are

1. Alkanes
2. Alkenes
3. Alkynes
4. All of them

Solution:

• Organic compounds, having only C and H atoms are called hydrocarbons.
• Alkanes, alkenes and alkynes all have only C and H atoms and fulfill the hydrocarbon’s definition criteria.
• Therefore, the answer is (All of them)

3. On the basis of type of bound present between carbon atoms, hydrocarbons are of

1. Two types
2. Three types
3. Four types
4. Five types

Solution:

• On the basis of type of bond present between carbon atoms, hydrocarbons are of three types.
• Namely; alkanes, alkenes and alkynes.
• Alkanes are the hydrocarbons have only single covalent bonds.
• Alkenes are the hydrocarbons have at least one double covalent bond.
• Alkynes are the hydrocarbons have at least one triple covalent bond.
• Therefore the answer is (Three types)

4. In saturated hydrocarbons

1. Only single covalent bonds are present
2. Single and double covalent bonds are present
3. Double and triple covalent bonds are present
4. Single, double and triple covalent bonds are present

Solution:

• The hydrocarbons in which all the carbon atoms are bounded together by single covalent bonds are called saturated hydrocarbons.
• Therefore, the answer is (only single covalent bonds are present)

5. In un-saturated hydrocarbons

1. Only single covalent bonds are present
2. Single and double covalent bonds are present
3. Double and triple covalent bonds are present
4. Single, double and triple covalent bonds are present

Solution:

• Hydrocarbons in which except single covalent bonds at least one double or triple covalent bond is present between any of two carbon atoms, are called unsaturated hydrocarbons.
• Therefore, the answer is (single, double and triple covalent bonds are present)

6. Saturated hydrocarbons are

1. Alkanes
2. Alkenes
3. Alkynes
4. Both a and b

Solution:

• The hydrocarbons in which all the carbon atoms are bounded together by single covalent bonds are called saturated hydrocarbons.
• And alkanes are organic compounds that have only single covalent bonds, not double or triple covalent bonds.
• Therefore, the answer is (alkanes)

7. Un-saturated hydrocarbons are

1. Alkanes
2. Alkenes
3. Alkynes
4. Both b and c

Solution:

• Organic compounds in which at least one double or triple covalent bond is present between any of two carbon atoms, are called unsaturated hydrocarbons.
• Alkenes are the organic compounds having at least one double covalent bond between any of two carbons.
• And alkynes are compounds having at least one triple covalent bond between any of two carbon atoms.
• So, both alkene and alkyne are unsaturated.
• Therefore, the answer is (both b and c)

8. General formula for alkanes is

1. C_nH_2n+2
2. C_nH_2n
3. C_nH_2n-2
4. None of them

Solution:

• General formula for alkane is C_nH_2n+2
• n is the number of carbon atoms and is equal to n = 1, 2, 3………
• If n = 1 then C₁H_2×1+2 = C₁H₂₊₂ = CH₄ (methane)
• If n = 2 then C₂H_2×2+2 = C₂H₄₊₂ = C₂H₆ (Ethane)
• Therefore, the answer is (C_nH_2n+2)

9. Non-polar hydrocarbons are

1. Alkanes
2. Alkenes
3. Alkynes
4. All of them

Solution:

• Hydrocarbons have only C and H atoms.
• The electronegativity difference between C and H atoms is very, very small.
• Due to the small electronegativity difference, the hydrocarbons are non-polar in nature and we know that all three alkanes, alkenes and alkynes are hydrocarbons.
• So, all three are non-polar.
• Therefore the answer is (all of them)

10. Hydrocarbons are non-polar due to

1. High electronegativity difference between C and H
2. Low electronegativity difference between C and H
3. Both a and b
4. None of them

Solution:

• The hydrocarbons have only C and H atoms and there is very small electronegativity difference between them.
• That’s why they are non-polar in nature.
• Therefore, the answer is (low electronegativity difference between C and H)

11. In alkanes the carbon atoms are linked together by

1. Single covalent bond
2. Double covalent bond
3. Triple covalent bond
4. All of the above

Solution:

• Alkanes are those organic compounds in which only single covalent bonds are present between carbon atoms.
• Therefore, the answer is (single covalent bond)
• A single covalent bond is a bond in which atoms share one pair of electrons.

12. Alkenes can be  defined as compounds in which carbon atoms are inked together by at least one

1. Single covalent bond
2. Double covalent bond
3. Triple covalent bond
4. All of the above

Solution:

• Alkenes are those organic compounds in which at least one double covalent bond is present between any two carbon atoms.
• Therefore, the answer is (double covalent bond)
• A double covalent bond is a bond in which atoms share two pairs of electron.

13. Alkynes can be  defined as compounds in which carbon atoms are inked together by at least one

1. Single covalent bond
2. Double covalent bond
3. Triple covalent bond
4. All of the above

Solution:

• Alkynes are those organic compounds in which at least one triple covalent bond is present between any two carbon atoms.
• Therefore, the answer is (triple covalent bond)
• A triple covalent bond is a bond in which atoms share three pairs of electron.

14. According to like dissolve like rule polar compounds are soluble in

1. Polar solvents
2. Non-polar solvents
3. Both a and b
4. None of them

Solution:

• There is a general rule of solubility, called like dissolve like rule.
• According to this rule polar compounds are soluble in polar solvents.
• And non-polar substances are soluble in non-polar solvents.
• Therefore, the answer is (polar solvents)

15. According to like dissolve like rule non-polar compounds are soluble in

1. Polar solvents
2. Non-polar solvents
3. Both a and b
4. None of them

Solution:

• There is a general rule of solubility, called like dissolve like rule.
• According to this rule polar compounds are soluble in polar solvents.
• And non-polar substances are soluble in non-polar solvents.
• Therefore, the answer is (non-polar solvents)

16. Hydrocarbons (non-polar organic compounds) are soluble in

1. Methanol
2. Ethanol
3. Benzene
4. Both a and b

Solution:

• Hydrocarbons are non-polar in nature
• According to like dissolve like rule, they will dissolve in non-polar solvent like benzene, not in polar solvents like methanol and ethanol.
• Therefore, the answer is (benzene)

17. According to IUPAC names are assigned to

1. Alkanes
2. Alkenes
3. Alkynes
4. All of them

Solution:

• International union of pure and applied chemistry assign names to each class of organic compounds either they are alkanes, alkenes or alkynes.
• Therefore, the answer is (all of them)

18. General formula for alkenes is

1. C_nH_2n+2
2. C_nH_2n
3. C_nH_2n-2
4. None of them

Solution:

• General formula for alkene is C_nH_2n
• n is the number of carbon atoms and is equal to n = 1, 2, 3………
• If n = 2 then C₂H_2×2 = C₂H₄ = C₂H₄ (Ethene)
• If n = 3 then C₃H_2×3  = C₃H₆ = C₃H₆ (Propene)
• Therefore, the answer is (C_nH_2n)

19. General formula for alkynes is

1. C_nH_2n+2
2. C_nH_2n-2
3. C_nH_2n
4. None of them

Solution:

• General formula for alkane is C_nH_2n-2
• n is the number of carbon atoms and is equal to n = 1, 2, 3………
• If n = 2 then C₂H_2×2-2 = C₂H_4-2 = C₂H₂ (Ethyne)
• If n = 3 then C₃H_2×3-2 = C₃H_6-2 = C₃H₄ (Propyne)
• Therefore, the answer is (C_nH_2n-2)

20. The bond most commonly present in organic compounds is

1. Ionic bond
2. Covalent bond
3. Coordinate covalent bond
4. Dipole-dipole interactions

Solution:

• Carbon is present in fourth group of periodic table.
• So, there are four electrons in its outermost electron.
• To complete its octet, carbon requires four another electrons.
• Therefore carbon will complete its octet by sharing four electrons with another atoms.
• And we know that, a bond formed by sharing of electrons between two carbon atoms is called covalent bond.
• Therefore, the answer is (covalent bond)

21. In alkanes the carbon atoms are linked together by

1. Single covalent bond
2. Double covalent bond
3. Triple covalent bond
4. All of the above

Solution:

• Alkanes are those organic compounds in which only single covalent bonds are present between carbon atoms.
• Therefore, the answer is (single covalent bond)
• A single covalent bond is a bond in which atoms share one pair of electrons.

22. Alkenes can be  defined as compounds in which carbon atoms are linked together by at least one

1. Single covalent bond
2. Double covalent bond
3. Triple covalent bond
4. All of the above

Solution:

• Alkenes are those organic compounds in which at least one double covalent bond is present between any two carbon atoms.
• Therefore, the answer is (double covalent bond)
• A double covalent bond is a bond in which atoms share two pairs of electron.

23. Alkynes can be  defined as compounds in which carbon atoms are linked together by at least one

1. Single covalent bond
2. Double covalent bond
3. Triple covalent bond
4. All of the above

Solution:

• Alkynes are those organic compounds in which at least one triple covalent bond is present between any two carbon atoms.
• Therefore, the answer is (triple covalent bond)
• A triple covalent bond is a bond in which atoms share three pairs of electron.

24. Methods used for preparation of alkanes are

1. Hydrogenation of alkenes and alkynes
2. Reduction of alkyl halides
3. Dehydration of alcohols
4. Both a and b

Solution:

Both the reduction of alkyl halide methods and the hydrogenation of alkenes and alkynes are utilized to prepare alkanes. Therefore, the answer is (both a and b).

By Hydrogenation of alkene and alkyne:

By reduction of alkyl halides:

25. The methods used for preparation of alkenes are

1. Dehydration of alcohols
2. Reduction of alkyl halides
3. Dehydrohalogenation of alkyl halides
4. Both a and c

Solution:

• Dehydration of alcohols and dehydrogenation of alkyl halides are both processes used to prepare alkenes.
• Therefore, the answer is (both a and c).

By dehydration of alcohol:

Example 1:

Example 2:

By dehydrohalogenation of alkyl halides:

26. The methods used for preparation of alkynes are

1. Dehydrohalogenation of vicinal di-halide
2. Addition of halogens
3. Dehydrohalogenation of alkyl halides
4. Both a and b

Solution:

Both the dehydrohalogenation of vicinal di-halide and the addition of halogen approaches are utilized to prepare alkynes. Therefore, the answer is (both a and b)

By dehydrohalogenation of vicinal di-halides:

By dehalogenation of tetra-halides:

27. Reaction perform by alkanes

1. Halogenation reaction
2. Combustion reaction
3. Reaction with KMnO₄
4. Both a and b

Solution:

• Alkanes perform both halogenation and combustion reactions.
• Therefore, the answer is (both a and b)

Combustion reaction:

Complete combustion reaction:

Incomplete combustion reaction:

Halogenation reaction:

28. Reaction perform by alkenes

1. Reaction with halogens
2. Combustion reaction
3. Reaction with KMnO₄
4. Both a and c

Solution:

• Alkynes perform reactions with both halogens and with KMnO₄.
• Therefore, the answer is (Both a and c).

29. Reaction perform by alkynes

1. Reaction with halogens
2. Dehydrohalogenation of alkyl halides
3. Reaction with KMnO₄
4. Both a and c

Solution:

• Alkynes perform reactions with both halogens and with KMnO₄.
• Therefore, the answer is (both a and c).

30. Combustion reaction is of

1. One type
2. Two types
3. Three types
4. Four types

Solution:

• Combustion reaction is of two type. One is complete combustion reaction.
• Second is incomplete combustion reaction.
• Complete combustion reaction takes place in the presence of excess oxygen gas.
• While in-complete combustion reaction takes place in the presence of limited oxygen gas.
• Therefore, the answer is (two types)

31. The products of complete combustion are

1. CO₂
2. Water
3. Heat
4. All of the above

Solution:

• The products of complete combustion are, CO₂, water and heat.
• Therefore, the answer is (all of the above)

32. The products of incomplete combustion are

1. CO
2. C
3. CO₂
4. Both a and b

Solution:

Products of incomplete combustion are CO and C. Therefore, the answer is (both a and b)

33. Complete combustion takes place in the presence of

1. Excess CO₂ gas
2. Excess O₂ gas
3. Limited O₂ gas
4. Limited CO₂ gas

Solution:

Complete combustion reaction takes place in the presence of excess oxygen gas. Therefore, the answer is (Excess O₂ gas).

34. Incomplete combustion takes place in the presence of

1. Excess CO₂ gas
2. Excess O₂ gas
3. Limited O₂ gas
4. Limited CO₂ gas

Solution:

In-complete combustion reaction takes place in the presence of limited oxygen gas. Therefore, the answer is (Limited O₂ gas).

35. Chlorination of alkanes takes place

1. In the presence of sunlight
2. In the absence of sunlight
3. In the presence of O₂
4. In the absence of O₂

Solution:

• Chlorination of alkanes takes place in the presence of sunlight.
• The presence of sunlight is necessary because chlorine gives slow reaction at room temperature.
• Therefore, the answer is (In the presence of sunlight)

36. Fossil fuels are

1. Coal
2. Natural gas
3. Petroleum
4. All of the above

Solution:

Coal, natural gas, and petroleum are all referred to as fossil fuels because they were extracted from the petrified, buried remains of plants and animals that once lived millions of years ago. Therefore, the answer is (all of the above)

37. Greenhouse effect is caused by

1. CO₂
2. CH₄
3. Both a and b
4. None of them

Solution:

The greenhouse effect is the condition in which “greenhouse gases” trap heat near the surface of the earth. CO₂ and methane are the greenhouse gases. Therefore the answer is (Both a and b).

38. CO₂ released into the air each year is

1. 20 billion tons
2. 25 billion tons
3. 30 billion tons
4. 40 billion tons

Solution:

According to records, nearly 25 billion tons of carbon dioxide are released into the atmosphere each year. Therefore, the answer is (25 billion tons).

39. In electron cross and dot formula show

1. C atoms by cross and H atoms by dots
2. C atoms by dots and H atoms by cross
3. One C atom by dot and another C atom by cross
4. One H atom by dot and another H atom by cross

Solution:

• In electron dot and cross structure formula valence electrons of carbon are represented as dots, and valence electrons of H atom are represented as cross.
• Therefore, the answer is (C atoms by dots and H atoms by cross)

40. Which gas is used as a fuel in cylinders and automobiles

1. CH₄
2. C₂H₆
3. C₃H₈
4. C₄H₁₀

Solution:

Methane is the gas used as fuel in cylinders and automobiles. Therefore, the answer is (CH₄).

41. Which compound has a double bond between carbon atoms?

1. Ethane
2. Ethene
3. Ethyne
4. Ethyl alcohol

Solution:

The hydrocarbons with at least one C-C double bond are known as alkenes. Ethene, the second member of the alkene family with a C-C double bond, is also present. Therefore, the answer is (ethene)

42. When chloromethane (or methyl chloride) is reduced, what is the final outcome?

1. Ethan
2. Ethene
3. Methane
4. Ethyne

Solution:

When methyl chloride is reduced then methane is produced as a product. Therefore, the answer is (Methane).

43. Which of these interacts violently with methane?

1. F₂
2. Cl₂
3. Br₂
4. I₂

Solution:

Florine reacts explosively with methane. Therefore the answer is (F₂).

 44.  Dehydration is the loss of

Hydrogen

Water

Halogen

Hydrogen halide

Solution:

• Hydra means water and de means removal.
• So, dehydration means removal of water.
• Therefore, the answer is (water).

45. One way to distinguish between ethene and ethyne is by

1. Hydrogenation
2. Bromine water
3. Strong alkaline aqueous solution of KMnO₄
4. Hydro halogenation

Solution:

• Bromine water can discriminate between ethene and ethyne.
• Ethene is used to treat bromine water, which prevents the brown coloration from dissipating.
• However, bromine water loses its brown coloration when it is treated with ethyne.
• Therefore, the answer is (bromine water)

46. For dehydrohalogenation, what is used?

1. Br₂ water
2. Conc. H₂SO₄
3. Al₂O₃
4. Alcoholic KOH

Solution:

For dehydrohalogenation alcoholic KOH is used. Therefore, the answer is (alcoholic KOH)

47. Oxalic acid is produced when what material reacts with KMnO4?

1. Ethane
2. Ethene
3. Ethyne
4. Ethyl alcohol

Solution:

• Ethyne on reaction with KMnO₄ produces oxalic acid.
• Therefore, the answer is (Ethyne).

48. Alkyl halides are reduced when they come into contact with

1. Al₂O₃ at 350 ^oC
2. Conc. H₂SO₄ at 170 ^oC
3. Zn + Dust
4. Zn + HCl

Solution:

Reduction of alkyl halide takes place in the presence of Zn + HCl. Therefore, the answer is Zn + HCl.

49. What generates an alkane?

1. Combustion
2. Hydration
3. Dehydration
4. Hydrogenation

Solution:

Hydrogenation (addition of hydrogen to alkene or alkyne) leads to the production of alkanes. Therefore the answer is (Hydrogenation).

50.  Not affected by bromine aqueous solution

1. C₂H₆
2. C₂H₄
3. C₂H₂
4. C₃H₆

Solution:

• The reaction of bromine with hydrocarbons is an addition reaction.
• Alkanes are saturated hydrocarbons only single covalent bonds are present in them.
• Therefore, no addition reaction takes place in alkanes.
• C2H6 is ethane, the second member of the alkane family, and because of its saturated state, it does not react with bromine water, which means no additional reaction is possible in it.
• Therefore, the answer is (C₂H₆).

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