Which oxide of $Mn$ is acidic in nature?

$A$ hard and resistant metal alloy generally used in the tip of the nib of a fountain pen is

Which of the following is used in the manufacture of high refractive index optical glass for cameras?

Thermal decomposition of a $Mn$ compound $(X)$ at $513 \ K$ results in compound $Y$,$MnO_2$ and a gaseous product. $MnO_2$ reacts with $NaCl$ and concentrated $H_2SO_4$ to give a pungent gas $Z$. Identify $X, Y$ and $Z$.

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

$ZnO \cdot CoO$ is called