Question

Arrange the following in decreasing order of their boiling points:
(I) $n$-Butane
(II) $2$-Methylbutane
(III) $n$-Pentane
(IV) $2$,$2$-Dimethylpropane

• A. $I>II>III>IV$
• B. $II>III>IV>I$
• C. $IV>III>II>I$
• D. $III>II>IV>I$

Answer 1

Answer: (D)

Boiling point of alkanes increases with increase in molecular mass and for the same alkane the boiling point decreases with branching.
Thus, the decreasing order of their boiling points is :
$\underset{(III)}{n-\text{Pentane}>}\underset{(II)}{2-\text{Methylbutane}>}\underset{(IV)}{2,2-\text{Dimethylpropane}>}\underset{(I)}{n-\text{Butane}}$