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-6O4I20+SO2-4+2H2O
Cu0+2H2SO4+6Cu+2SO4+SO2+4+2H2O