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

Equivalent weight of $KMnO_4$ acting as an oxidant in acidic medium is

Oxidation number of osmium $(Os)$ in $OsO_4$ is

Assertion: The average oxidation number of sulfur in $Na_2S_4O_6$ is $2.5$.
Reason: Two $S$ atoms are not directly bonded to $O$-atoms.

What are the respective oxidation states of sulphur atoms numbered $1$ to $4$ in the tetrathionate ion $(S_4O_6^{2-})$ shown below?

Given below are two statements.
Statement $I$ : In $H_2O_2$, each oxygen atom is assigned an oxidation number of $-1$, and in $RbO_2$, each oxygen atom is assigned an oxidation number of $-\frac{1}{2}$.
Statement $II$ : The representation of $HAuCl_4$ and $MnO_2$ in Stock notation is $HAu(III)Cl_4$ and $Mn(IV)O_2$ respectively.
Examine the above statements and choose the correct answer.