When zinc reacts with dilute $HNO_3$,the oxidation state of nitrogen changes from

Oxidation state of sulphur in tetrathionic acid is

In alkaline condition,$KMnO_4$ reacts as $2KMnO_4 + 2KOH \to 2K_2MnO_4 + H_2O + [O]$. The equivalent weight of $KMnO_4$ would be (Atomic mass of $K = 39$,$Mn = 55$,$O = 16$).

What is the oxidation number of carbon in methanal?

In which one of the following changes is there a transfer of five electrons?

The compound $YBa_2Cu_3O_7$,which shows superconductivity,has copper in an oxidation state of ........ Assume that the rare earth element Yttrium is in its usual $+3$ oxidation state.