In which of the following reactions conc. H2SO4 is used as an oxidising reagent?

a. CaF2   +   H2SO4   →   CaSO4   +   2 HF
2. 2HI   +  H2SO4   →   I2   +   SO2   +   2H2O
3. Cu +  2H2SO4   →   CuSO4   +   SO2   +   2H2O
4.

NaCl + H2SO4  NaHSO4 + HCl

Choose the correct option:

1. (a, b) 2. (b, c)
3. (c, d) 4. (a, d)
 
 



Hint: Oxidising agent oxidized other, and itself gets reduced.

In the above given four reactions, (b) and (c) represent oxidizing behaviour of H2SO4 . As we know that oxidizing agent reduces itself as the oxidation state of the central atom decreases. Here, 
2HI-1 + H2S-6O4  I20 + SO2-4 + 2H2O
Cu0 + 2H2SO4+6  Cu+2SO4 + SO2+4 + 2H2O