The Volume of an ideal gas is 1 liter column and its Pressure is equal to $72 \mathrm{~cm}$ of $\mathrm{Hg}$. The Volume of gas is made 900 $\mathrm{cm}^{3}$ by compressing it isothermally. The stress of the gas will be $\ldots \ldots \ldots \ldots .$ Hg column.
(A) $4 \mathrm{~cm}$
(B) $6 \mathrm{~cm}$
(C) $7 \mathrm{~cm}$
(D) $8 \mathrm{~cm}$