Determine the oxidation state of $Cr$ in $K_2Cr_2O_7$.

In the following reaction,assign the oxidation state of the underlined atom for the product of complete hydrolysis at $R.T.$:
$H\underline{N}O_4 + H_2O \longrightarrow HNO_3 + H_2O_2$

Oxidation number of osmium $(Os)$ in $OsO_4$ is

The oxidation number of carbon in $H_2C_2O_4$ is:

Match the following:

Compound	Oxidation number
$1$. $CrO_5$	$a$. $+6$
$2$. $H_2SO_4$	$b$. $+1$
$3$. $C_4OCl_2$	$c$. $-1$
$4$. $(CH_3)_2SO$	$d$. $+2$

What is the change in the oxidation state of $Mn$ in the reaction of $MnO_4^{-}$ with $H_2O_2$ in acidic medium?