Select the compound in which chlorine is assigned the oxidation number $+5$.

The oxidation number of sulphur in $S_2O_3^{2-}$ is:

What is the oxidation number of carbon in $CH_2Cl_2$?

What is the oxidation number of $Cl$ in bleaching powder?

The oxidation number of an element in a compound is evaluated on the basis of certain rules. Which of the following rules is not correct?
$1$. The oxidation number of hydrogen is always $+1$.
$2$. The algebraic sum of all the oxidation numbers of all elements in a compound is zero.
$3$. An element in the free or the uncombined state bears oxidation number zero.
$4$. In all its compounds,the oxidation number of fluorine is $-1$.

When $K_2Cr_2O_7$ is converted to $K_2CrO_4$,the change in the oxidation state of chromium is