$H_2O_2$ is obtained by which of the following?

In which of the following reactions does $H_2O_2$ act as a reducing agent?
$(I)$ $H_2O_2 + 2H^{+} + 2e^- \to 2H_2O$
$(II)$ $H_2O_2 \to O_2 + 2H^{+} + 2e^-$
$(III)$ $H_2O_2 + 2e^- \to 2OH^{-}$
$(IV)$ $H_2O_2 + 2OH^{-} \to O_2 + 2H_2O + 2e^-$

What is the order of $K_a$ for $H_2O_2$?

By which of the following methods,$H_2O_2$ cannot be synthesized?

$H_2O_2$ (hydrogen peroxide),in the pure state,is:

$H_2O_2$ is