The boiling points of HF, H2O and NH3 increase in the order of

Analyze the question: The question asks for the order of increasing boiling points of HF, H₂O and NH₃. Options A and B are incomplete (they look truncated), so the real choice is between C and D.

Concept: All three compounds have hydrogen bonding, so their boiling points are much higher than expected for their molar masses. The strength of the hydrogen bonding depends on two things:

1. How electronegative the atom bonded to H is (N < O < F).
2. How many hydrogen bonds each molecule can form on average.

Step by step:

• NH₃: N is the least electronegative of the three, so its hydrogen bonds are the weakest. Each molecule has only one lone pair, which limits the network. Boiling point = -33 °C.
• HF: F is the most electronegative, so its hydrogen bonds are the strongest. But each F has only one H, so it forms just chains or zigzag rings, not a 3D network. Boiling point = 19.5 °C.
• H₂O: Each molecule has 2 H atoms and 2 lone pairs, so it can form up to 4 hydrogen bonds. This gives an extensive 3D network. Boiling point = 100 °C.

Order of increasing boiling point:

NH₃ (-33 °C) < HF (19.5 °C) < H₂O (100 °C)

This matches option D.

Answer: D

Tip: Remember the boiling points as -33, 19.5, 100, and think "No Fun Overheating", giving the order N, F, O from lowest to highest. Water wins because the number of hydrogen bonds per molecule matters as much as their strength.