Out of $Cu_2Cl_2$ and $CuCl_2$, which is more stable and why ?

Solder is an alloy of

Assertion : Transition metals are good catalysts.

Reason : $V_2O_5$ or $Pt$ is used in the preparation of $H_2SO_4$ by contact process.

The second and third rows of transition elements resemble each other much more than they resemble the first row. Explain why ?

Bullet-proof steel alloy is prepared by using

A pink colored salt on dry heating becomes blue in colour. Salt may contain