Units and Measurements: JEE Main 2023 Physics question

In the equation $\left[X+\frac{a}{Y^{2}}\right][Y-b]=\mathrm{R} T, X$ is pressure, $Y$ is volume, $\mathrm{R}$ is universal gas constant and $T$ is temperature. The physical quantity equivalent to the ratio $\frac{a}{b}$ is: