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JEE Advanced levelSingle correct optionDifficulty 3 of 3cb215

The boiling points of Group $16$ hydrides are $H X_{2} O$ $373 K$ , $H X_{2} S$ $213 K$ , $H X_{2} Se$ $232 K$ and $H X_{2} Te$ $271 K$ . Which statement correctly accounts for this trend?

A $H X_{2} O$ is hydrogen bonded, while from $H X_{2} S$ to $H X_{2} Te$ the increasing polarisability strengthens dispersion forces
BThe rise from $H X_{2} S$ to $H X_{2} Te$ is caused by increasing hydrogen bonding
C $H X_{2} O$ is highest because it has the greatest molar mass
D $H X_{2} S$ boils lower than $H X_{2} Se$ because it has a larger molar mass

Answer: A

The molar mass of

H X_{2} O

is the smallest in the series, so its high boiling point must come from hydrogen bonding. S, Se and Te are not electronegative enough for significant hydrogen bonding. Their boiling points rise with molar mass and polarisability because London forces grow stronger.

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