Q.Assertion: Boiling points of alcohols and ethers are high.
Reason: They can form intermolecular hydrogen-bonding.

Hydrogen bonding raises boiling points, but the effect is not equal for alcohols and ethers.

1. Alcohols have an -OH group and form strong intermolecular hydrogen bonds, giving them high boiling points. …

Reasoning

Alcohols (R-OH) can both donate and accept hydrogen bonds, giving strong intermolecular association and high boiling points relative to hydrocarbons of similar mass. Ethers (R-O-R') have no O-H bond and so cannot donate a hydrogen bond to another ether molecule; their boiling points are much closer to those of alkanes of similar size (e.g. dimethyl ether boils at about -24 degC, well below room temperature). So the claim that boiling points of alcohols …

Method: Assertion–Reason Analysis (Conceptual Verification)

Step 1 – Identify the concept tested

The question checks your understanding of boiling point trends in alcohols and ethers, specifically the role of intermolecular hydrogen bonding.

Step 2 – Verify the Assertion

• Alcohols (e.g., ethanol, propanol) have high boiling points because they form strong intermolecular H-bonds between —OH groups.
• Ethers (e.g., diethyl ether) have much lower boiling points than alcohols of similar molecular mass.
  • Example: Ethanol (M = 46, bp = 78°C) vs. Dimethyl ether (M = 46, bp = −24°C).
• Conclusion: The assertion “Boiling points of alcohols and ethers are high” is incorrect — ethers do not have high boiling points.

Step 3 – Verify the Reason

• Alcohols can form intermolecular H-bonds (due to —OH group). …

Here are the common mistakes students make on this exact question, along with how to avoid each.

Mistake 1: Assuming the Assertion is Completely True

The error: Students think "high boiling point" means all alcohols and ethers have high boiling points. They miss the nuance that ethers have significantly lower boiling points than alcohols of comparable molar mass.

How to avoid:

• Remember: Alcohols have high boiling points due to strong intermolecular hydrogen bonding.
• Ethers have much lower boiling points than alcohols (though still higher than alkanes of similar size) because they can only accept hydrogen bonds, not donate them.
• The assertion says "boiling points of alcohols and ethers are high" — this is too broad and therefore wrong for ethers.

Key fact:

• Ethanol (alcohol) boils at 78°C
• Dimethyl ether (ether, same formula) boils at −24°C
• That’s a 102°C difference — ethers are not "high boiling."

Mistake 2: Thinking the Reason is Wrong

The error: Some students think hydrogen bonding is not the reason for high boiling points, or they confuse it with covalent bonding.

How to avoid:

• Intermolecular hydrogen bonding is the correct reason for the high boiling points of alcohols.
• The reason statement is scientifically correct — it just doesn’t explain the assertion because the assertion itself is flawed.

Mistake 3: Choosing Option (A) — Both correct, reason explains assertion

The error: Students see "hydrogen bonding → high boiling point" and think it’s a perfect match, ignoring that ethers don’t fit.

How to avoid:

• Always check if the assertion applies to both substances mentioned.
• If one part of the assertion is false, the whole assertion is false.
• Here, ethers break the assertion, so (A) is impossible.

Mistake 4: Choosing Option (B) — Both correct, but reason doesn’t explain

The error: Students accept the assertion as true and then say the reason is correct but not the explanation — but the assertion is actually wrong.

How to avoid:

• Never assume an assertion is true just because it sounds plausible.
• Test with a concrete example: compare ethanol and dimethyl ether.

Mistake 5: Choosing Option (C) — Assertion correct, reason wrong

The error: Students think hydrogen bonding is not the reason, perhaps confusing it with covalent bond strength or van der Waals forces.

How to avoid: …