What is the correct relation between normality $\left(\mathrm{N}\right)$ and molarity $\left(\mathrm{M}\right)$ of $K_{2}C{r}_2{O}_7$ acting as oxidising agent in acidic medium?

The relation between the normality and molality is,

$\mathrm{N}=6\mathrm{M}$ 

$\mathrm{Cr}+6$ converts to$\mathrm{Cr}+3$ since $K_{2}C{r}_2{O}_7$ is an oxidising agent it undergoes reduction i.e decrease in oxidation state.

The factor for oxidizing and reducing agent is the total number of electrons gained or lost during a reaction. For the above the total electrons gained will be,
$(2x+6)-(2x+3)=6$
$x=6$

Hence, option A is correct.