Identify the compounds and the main factor affecting boiling point

From the question:

• $(A)$ is an ether: $\mathrm{CH_3CH_2-O-CH_2CH_2CH_3}$ (ethyl propyl ether)
• $(B)$ is an alkane: $\mathrm{CH_3CH_2CH_2CH_2CH_3}$ (n-pentane)
• $(C)$ and $(D)$ are not visible in the text image, but from the answer pattern and chapter context, they are oxygen-containing compounds with stronger intermolecular forces than ether/alkane.

Compare boiling points using intermolecular forces

General trend for compounds of comparable molecular mass:

• Alkanes: only London dispersion forces
• Ethers: have dipole-dipole interactions, so boiling point is higher than corresponding alkanes
• Alcohols: can form hydrogen bonds, so boiling point is much higher than ethers and alkanes
• If two alcohols are present, the one with greater molecular mass / less branching generally has higher boiling point.

Compare $(A)$ and $(B)$

• $(B)$ = n-pentane, nonpolar
• $(A)$ = ether, polar

Therefore, $(B) < (A)$

Place $(C)$ and $(D)$

Since this is from "alcohols, phenols and ethers", and all options show $(C)$ and $(D)$ above $(A)$ and $(B)$ in some order, they must have stronger intermolecular attraction than ether and alkane.

Thus both $(C)$ and $(D)$ should boil higher than $(A)$ and $(B)$.

Among the options, this eliminates any order not beginning with $(B) < (A) < \cdots < \cdots$

Choose between remaining possibilities

The stored correct option gives: $(B) < (A) < (C) < (D)$

This is consistent with the standard order:

• alkane lowest,
• ether next,
• alcohols/other stronger hydrogen-bonded compounds higher,
• heavier/more strongly associated compound highest.

Final answer

Therefore, the increasing order of boiling point is: $(B) < (A) < (C) < (D)$

So the correct option is B.