For the Compounds :
(A) H₃ C-CH₂-O-CH₂-CH₂-CH₃
(B) H₃ C-CH₂-CH₂-CH₂-CH₃
(C) CH₃-CH₂-C-CH₂-CH₃
(D) H₃C-CH-CH₂-CH₂-CH₃
The increasing order of boiling point is :
Choose the correct answer from the options given below :

Solution

Chemistry ma’am · 3 steps

The molar masses are close, so rank them by the strongest force between molecules.

1. Same size. All four have five carbons and molar masses of 72 to 88. Mass cannot separate them, so the type of intermolecular force decides the order.

   Compound	Molar mass	Strongest force	Boiling point
   (B) pentane	72	London forces only, non-polar	about 36 °C
   (A) ethyl propyl ether	88	weak dipole–dipole from the bent C–O–C	about 64 °C
   (C) pentan-3-one	86	strong dipole–dipole from the very polar C=O	about 102 °C
   (D) pentan-2-ol	88	hydrogen bonding through O–H	about 119 °C

2. Why this order. An ether has no O–H, so its molecules cannot hydrogen bond with each other. The C–O dipole is weak, which puts it only a little above the alkane. The C=O dipole is much stronger, but hydrogen bonding in the alcohol is stronger still.
3. So. The increasing order is (B) < (A) < (C) < (D), which is option (b).

The idea to keep. When molar masses are similar, boiling point follows the force: alkane < ether < aldehyde or ketone < alcohol. Only the alcohol has an O–H, so only the alcohol hydrogen bonds with itself.

Answer from the NTA final answer key. Solution by PrepWiser.