(a) O has smaller size than S due to which the O-O bond length is short which results in repulsion of lone pairs on O making it unstable and the bond can be cleaved. Whereas due to big size of S, no such repulsion is present and the S-S bond is stronger than that between O-O.
(b) Tendency to exhibit -3 oxidation state decreases down the group due to increase in size and metallic character.
(c) Chlorine water on standing loses its yellow colour due to the formation of HCl and HOCl. Hypochlorous acid (HOCl) so formed, gives nascent oxygen which is responsible for oxidising and bleaching properties of chlorine.
Cl2 + H2O → HCl + HOCl
HOCl → HCl + (O)
Coloured substance + (O) → Colourless substance
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