Which of the following mixtures is known as chromic acid?

Identify the reducing agent in the following chemical equations:
$4Ag(s) + 8CN^{-}(aq) + 2H_{2}O(aq) + O_{2}(g) \rightarrow 4[Ag(CN)_{2}]^{-}(aq) + 4OH^{-}(aq)$
$2[Ag(CN)_{2}]^{-}(aq) + Zn(s) \rightarrow [Zn(CN)_{4}]^{2-}(aq) + 2Ag(s)$

Statement $I$: Sodium hydride can be used as an oxidising agent.
Statement $II$: The lone pair of electrons on nitrogen in pyridine makes it basic.
Choose the $CORRECT$ answer from the options given below:

Which substance is serving as a reducing agent in the following reaction: $14H^{+} + Cr_2O_7^{2-} + 3Ni \to 2Cr^{3+} + 7H_2O + 3Ni^{2+}$?

While sulphur dioxide and hydrogen peroxide can act as oxidising as well as reducing agents in their reactions,ozone and nitric acid act only as oxidants. Why?

Identify the reducing agent in the following reaction:
$H_2O_{2(aq)} + ClO_{4(aq)}^{-} \rightarrow ClO_{2(aq)}^{-} + O_{2(g)}$