A reaction ${\mathrm{X}}_2\left(\mathrm{g}\right)\to \mathrm{Z}\left(\mathrm{g}\right)+\frac{1}{2}\mathrm{Y}\left(\mathrm{g}\right)$ exhibits an increase in pressure from 150 mm to 170 mm in 10 min. The rate of disappearance of X₂ in mm per min is ____.

$$\begin{gathered} {\mathrm{X}}_2\left(\mathrm{g}\right)\to \mathrm{Z}\left(\mathrm{g}\right)+\frac{1}{2}\mathrm{Y}\left(\mathrm{g}\right) \\ \begin{array}{l}{\mathrm{t}}_0\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em} 150\hspace{0.25em} \hspace{0.25em}\hspace{0.25em}\hspace{0.25em}0\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}0\end{array} \\ 10min150-\mathrm{x}\mathrm{x}\frac{\mathrm{x}}{2} \\ \text{ Total pressure }=150-\mathrm{x}+\mathrm{x}+\frac{\mathrm{x}}{2} \\ =150+\frac{\mathrm{x}}{2}=170\mathrm{x}=40\mathrm{mm} \\ \mathrm{Rate} \mathrm{of} \mathrm{disappearance} \mathrm{of} {\mathrm{X}}_2=\frac{40}{10}=4\mathrm{mm}/\min \end{gathered}$$