Which of the following is not the application of $\text{PCR}$?

The mass of oxygen gas occupying a volume of $11.2 \text{ litres}$ at a temperature $27^{\circ}C$ and a pressure of $760 \text{ mm}$ of mercury in kilograms is $[$Molecular weight of oxygen $= 32]$

The ratio $C_p/C_v$ for a gas mixture consisting of $8 \ g$ of helium and $16 \ g$ of oxygen is

$A$ chloro compound of Vanadium has a spin-only magnetic moment of $1.73 \, BM$. This Vanadium chloride has the formula:

$A$ block rests on a rough inclined plane making an angle of $30^o$ with the horizontal. The coefficient of static friction between the block and the plane is $0.8$. If the frictional force on the block is $10 \, N$,the mass of the block (in $kg$) is (take $g = 10 \, m/s^2$)

Which one of the following gives a straight line for Freundlich adsorption isotherm?