Chrome yellow is chemically known as

When an oxide of manganese $(A)$ is fused with $KOH$ in the presence of an oxidising agent and dissolved in water,it gives a dark green solution of compound $(B)$. Compound $(B)$ disproportionates in neutral or acidic solution to give purple compound $(C)$. An alkaline solution of compound $(C)$ oxidises potassium iodide solution to a compound $(D)$ and compound $(A)$ is also formed. Identify compounds $A$ to $D$ and also explain the reactions involved.

In making gun-barrel,the steel used is

On heating $KMnO_4$,which one of the following is not formed?

The spin-only magnetic moment value of the most basic oxide of vanadium among $V_2O_3$,$V_2O_4$,and $V_2O_5$ is $..... \ B.M.$ (Nearest Integer).

When copper turnings and concentrated $HCl$ are heated with copper sulphate,the compound formed is: