Two consecutive members of a homologous series differ by
- A.CH2 and 14 units of mass
- B.CH3 and 15 units of mass
- C.C2H4 and 28 units of mass
- D.CH4 and 16 units of mass
Correct answer
Explanation
The correct answer is A, a CH2 unit and fourteen units of mass. Going from methane to ethane, or from ethanol to propanol, adds one carbon atom of mass twelve and two hydrogen atoms of mass one each, which is fourteen in all, and it is this fixed step that defines a homologous series. Option B is wrong because CH3 is a group, not the difference between successive members; a compound cannot differ from another by an odd fragment of this kind and remain a stable molecule of the same series. Option C is wrong because C2H4 would be a jump of two members at once, skipping one homologue. Option D is wrong because CH4 is the whole molecule of methane rather than the step of the series. Members of such a series share the same functional group and show a gradual change in boiling point and density.
Read the full article: Carbon and Its Compounds: Bonding, Allotropes and PYQs
Practice Questions
View allCooking gas (LPG) mainly consists of
- A.Ethene
- B.Ethyne
- C.Propene
- D.Propane and Butane
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Liquefied petroleum gas is a mixture of these two saturated hydrocarbons, which are gases at ordinary pressure but turn liquid under moderate pressure, so a large quantity of fuel fits into a small cylinder; a strong-smelling compound is added so that a leak is noticed.
Read the full explanation →How many isomers does C6H14 have?
- A.3
- B.6
- C.4
- D.5
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Hexane, C6H14, can be drawn as a straight chain of six carbons, as two chains of five carbons with a methyl branch in different positions, and as two chains of four carbons carrying branches, which gives five different structures with the same molecular formula.
Read the full explanation →Compounds with exactly two double carbon to carbon bonds are known as ______.
- A.Terpenes
- B.Dienes
- C.Trialkyne
- D.Dialkyne
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The prefix di stands for two and the ending ene for a carbon to carbon double bond, so a diene is a hydrocarbon carrying exactly two such bonds; buta-1,3-diene, the raw material of synthetic rubber, is the standard example.
Read the full explanation →The first member of the alkyne group of hydrocarbons is
- A.propyne
- B.ethyne
- C.methyne
- D.butyne
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An alkyne contains a carbon to carbon triple bond, which needs at least two carbon atoms, so the series begins with ethyne, C2H2, also called acetylene and used with oxygen in welding.
Read the full explanation →A gas stove flame burns blue because of
- A.Complete combustion of fuel
- B.Presence of hydrogen in the air
- C.Hazardous combustion
- D.Insufficient oxygen
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When enough air reaches the burner, every carbon atom of the fuel is oxidised fully to carbon dioxide and the flame is blue and hot, giving the maximum heat for the gas consumed.
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