Identify the substance which acts as an oxidising agent and reducing agent in the following reaction :
(i) `H_(2)(g) +Cl_(2)(g) to 2HCl(g)`
(ii) `2Al(s) + Cr_(2)O_(3)(s) to Al_(2)O_(3)(s) +2Cr(s)`

Explanation

`Cl_(2)` in reaction (i) and `Cr_(2)O_(3)` in reaction (ii), acts as an oxidising agent.
While, `H_(2)` in reaction (i) and Al, in reaction (ii) acts as a reducing agent.