Answer any five of the following questions.
a) Given reason: (i) Hydrogen bonding in `H_2 O` but not in `H_2 S`
(ii) Conc. `H_2 SO_4` is a good dehydrating agent

Explanation

(a) (i) Since oxygen is more electronegative and has small size.
(ii) Due to strong affinity for water/it removes elements of water in the form of `H_2O`
(b)
Detailed Answer: 
(a) (i) (A) In water, the oxygen atom is highly electronegative and can polarize (partially) the hydrogen atoms, thus hydrogen-hydrogen bonds between the `H_2O` molecules results in the creation of a stable intermolecular network and the very high boiling point of water and alcohols. In `H_2S` those bonds don.t exist, because sulphur is much less electronegative.
(B) Another reason may be that O uses `sp^(3)` orbitals, and thus alone may be able to form stable hydrogen bonds. By comparison S use p orbitals, which may not be able to form stable hydrogen bonds. (Any other correct justification)
(ii) Because it has a strong affinity for water and thus it absorbs water quickly.
(b) In sulphurous acid, one atom of sulphur is bonded to two hydroxyl groups and one oxygen atom forms `a pi` bond with the sulphur atom.