Question

The acidity of hydrides of $O , S , Se$, Te varies in the order :

• A. $H _{2} O > H _{2} S > H _{2} Se > H _{2} Te$
• B. $H _{2} O < H _{2} S < H _{2} Se < H _{2} Te$
• C. $H _{2} S > H _{2} O > H _{2} Se > H _{2} Te$
• D. $H _{2} Se > H _{2} S > H _{2} O > H _{2} Te$

Answer 1

Answer: (B)

$H _{2} O < H _{2} S < H _{2} Se < H _{2} Te$

Answer 2

The acidic nature increases from $H _{2} O$ to $H _{2} Te$ The increase in acidic character of hydrides on moving down the group may be explained in terms of bond length of $H -M$ bond, larger is bond-length, lesser is bond energy and thus easier is ionisation of $H -M$ bond or easier is proton donor nature. Hence, $H _{2} O < H _{2} S < H _{2} Se < H _{2} Te$