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Carbon and its Compounds — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceCarbon and its Compounds1 Mark
Question
Two statements are given - one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
  1. Both A and Rare true and R is the correct explanation of the Assertion.
  2. Both A and R are true but R is not the correct explanation of the Assertion.
  3. A is true but R is false.
  4. A is false but R is true.
Assertion(A): In a homologous series of alcohols, the formula for the second member is C2H5OH and the third member is C3H7OH.

Reason(R): The difference between the molecular masses of the two consecutive members of a homologous series is 144.
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Answer

  1. A is true but R is false.

Explanation:

A homologous series is a series of organic compounds that contains identical functional group and differs only in the length of the carbon chain in the compound.

The general formula for homologous series for alcohols is C(n)H(2n + 1)OH, where n is a natural number.

Substituting n = 2 and n = 3 we get C2H5OH and C3H7OH respectively, which verifies the assertion made.

The two consecutive members of the homologous series varies only by a CH2 group, hence the difference in molecular mass of two consecutive members is equal to 14.

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