Question

Consider the following statements about homologous series of carbon compounds:
(a) All succeeding members differ by –CH₂ unit.
(b) Melting point and boiling point increases with increasing molecular mass.
(c) The difference in molecular masses between two successive members is 16 u.
(d) C₂H₂ and C₃H₄ are NOT the successive members of alkyne series.
The correct statements are –

• (a) and (b)
• (b) and (c)
• (a) and (c)
• (c) and (d)

Answer 1

The Correct Option is A

Step 1: Understanding the question:
The question asks about the correct statements regarding the homologous series of carbon compounds. Let's analyze each statement one by one.

Statement (a):
"All succeeding members differ by –CH₂ unit."
This statement is correct. In a homologous series, each successive member differs from the previous one by a –CH₂ unit, which is the simplest form of structural increment in organic compounds.

Statement (b):
"Melting point and boiling point increases with increasing molecular mass."
This statement is correct. As the molecular mass of compounds in a homologous series increases, their melting and boiling points generally increase due to stronger intermolecular forces (such as van der Waals forces) between molecules.

Statement (c):
"The difference in molecular masses between two successive members is 16 u."
This statement is incorrect. In an alkane homologous series, the difference in molecular masses between successive members is 14 u (because each successive member differs by a –CH₂ unit, which has a molecular mass of 14). For alkynes, the difference is also 14 u.

Statement (d):
"C₂H₂ and C₃H₄ are NOT the successive members of alkyne series."
This statement is correct. C₂H₂ (ethyne) and C₃H₄ (propene) are not successive members of the alkyne series. In fact, ethyne (C₂H₂) and propyne (C₃H₄) are the successive members of the alkyne series. The series follows a pattern where each compound differs by CH₂.

Step 2: Conclusion:
The correct statements are (a) and (b). Therefore, the correct answer is (a) and (b).