NEET 2022 — Chemistry solution

NEET2022Chemistry

Given below are two statements:

Statement I :

The boiling points of the following hydrides of group 16 elements increases in the order H $_{2}$ O $<$ H $_{2}$ S $<$ H $_{2}$ Se $<$ H $_{2}$ Te.

Statement II:

The boiling points of these hydrides increase with increase in molar mass.

In the light of the above statements, choose the most appropriate answer from the options given below:

A
Both Statement I and Statement II are incorrect
B
Statement I is correct but Statement II is incorrect
C
Statement I is incorrect but Statement II is correct
D
Both Statement I and Statement II are correct

Solution

Water is exceptional among the group 16 hydrides because of strong intermolecular hydrogen bonding, so it has the highest boiling point.

For H $_{2}$ S, H $_{2}$ Se, and H $_{2}$ Te, hydrogen bonding is negligible and van der Waals forces (which scale with molecular size) dominate. So among these three, boiling point rises with molar mass.

The complete experimental order is H $_{2}$ S $<$ H $_{2}$ Se $<$ H $_{2}$ Te $<$ H $_{2}$ O. The order in Statement I is incorrect.

Statement II is also incorrect as a general rule for the whole family because it ignores the anomalous behaviour of H $_{2}$ O caused by hydrogen bonding.

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