Give reason for the following within two sentences:
i. Hydrogen bromide cannot be prepared by the action of concentrated sulphuric acid on sodium bromide.
ii. When a blue litmus paper is dipped in a solution of hypochlorous acid, it first turns red then gets decolourised.

Explanation

i. `H_(2)SO_(4)+2HBr rarr SO_(2)+Br_(2)+2H_(2)O`
HBr is a stronger reducing agent, thus it reduces concentrated `H_(2)SO_(4)` into `SO_(2)` and itself gets oxidised to bromine.
ii. Hypochorous acid is acidic in nature, so it turns blue litmums red.
`HCIO rarr HCI+[O]`
It gives nascent oxygen, so it is also a bleaching agent, and the litmus gets decolourised.