The pair of compounds in which both the metals are in the highest possible oxidation state is

The oxidising ability of the given anions follows the order:

When a mixture of $NaCl$,$K_{2}Cr_{2}O_{7}$ and conc. $H_{2}SO_{4}$ is heated in a dry test tube,a red vapour $(X)$ is evolved. This vapour $(X)$ turns an aqueous solution of $NaOH$ yellow due to the formation of $Y$. $X$ and $Y$,respectively,are

What is the use of potassium permanganate $(KMnO_4)$?

The total number of $Mn=O$ bonds in $Mn_2O_7$ is

When dilute $H_2SO_4$ is added to an aqueous solution of potassium chromate,the yellow color of the solution turns to orange. What does this indicate?