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

Which of the following statements is not correct about $Cu^{2+}$ and $Cu^{+}$?

$A$ metal $M$ which is not affected by strong acids like conc. $HNO_3$,conc. $H_2SO_4$ and conc. solutions of alkalies like $NaOH$,$KOH$ forms $MCl_3$,which finds use for toning in photography. The metal $M$ is:

What is the starting material for the preparation of $KMnO_4$?

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

The presence of $Mn$ in steel produces