Which alloy is used for making statues and medals?

An element $A$ burns with a golden yellow flame in air. It reacts with another element $B$ (atomic number $17$) to give a product $C$. An aqueous solution of product $C$ on electrolysis gives a compound $D$ and liberates hydrogen. Identify $A$,$B$,$C$,and $D$. Also,write down the equations for the reactions involved.

What is the process of depositing a layer of gold on silver called?

What is the shape of rhombic sulphur?

Give reasons for the following:
$(i)$ Gold and platinum are used in jewellery.
$(ii)$ Copper cannot displace hydrogen from dilute acids.
$(iii)$ Stainless steel does not rust easily.
$(iv)$ Metals can be given different shapes according to our needs.
$(v)$ Zinc does not give hydrogen gas on reacting with $HNO_3$.

Explain the following:
$(a)$ The reactivity of $Al$ decreases if it is dipped in $HNO_3$.
$(b)$ Carbon cannot reduce the oxides of $Na$ or $Mg$.