Which of the following elements is doped into a fiber amplifier in an optical fiber communication system?

Identify $(A)$,$(B)$ and $(C)$ in the given reaction sequence:

When $XO_2$ is fused with an alkali metal hydroxide in the presence of an oxidizing agent such as $KNO_3$,a dark green product is formed which disproportionates in an acidic solution to afford a dark purple solution. $X$ is

Which mineral among the following contains Vanadium in it?

Which of the following imparts green colour to the glass?

Identify the wrong statement regarding copper$(II)$ sulphate $(CuSO_4)$.