$Orange-(A)$ (Inorganic compound) $+ H^{+} + H_2O_2 \to Blue-(B)$. The oxidation state of the central atom in compound $(B)$ is:

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

The highest oxidation state of $Mn$ is exhibited in $Mn_2O_7$. The correct statements about $Mn_2O_7$ are:
$(A)$ $Mn$ is tetrahedrally surrounded by oxygen atoms.
$(B)$ $Mn$ is octahedrally surrounded by oxygen atoms.
$(C)$ Contains $Mn-O-Mn$ bridge.
$(D)$ Contains $Mn-Mn$ bond.
Choose the correct answer from the options given below:

What are interstitial compounds? Give their examples and characteristics.

$Fe(OH)_2$ is precipitated from $Fe(II)$ solutions as a white solid but turns dark green and then brown due to the formation of:

Sodium chromate,$Na_2CrO_4$ is made commercially by