Given, Initial pressure of liquid $\left(\mathrm{P}_{\mathrm{i}}\right)=1 \mathrm{~atm}$

Final pressure of liquid $\left(\mathrm{P}_{\mathrm{f}}\right)=5 \mathrm{~atm}$

Change in pressure $(\mathrm{dP})=\mathrm{P}_{\mathrm{f}}-\mathrm{P}_{\mathrm{i}}=4 \mathrm{~atm}$

$$=4 \times 10^5 \mathrm{~Pa}$$

Change in volume $(\mathrm{dV})=-0.8 \mathrm{~cm}^3$

Bulk modulus $(B)=2 \times 10^9 \mathrm{~Pa}$

Now, $B=\frac{-d P}{(d V / V)} \Rightarrow V=-B\left(\frac{d V}{d P}\right)$

$$\begin{aligned} \Rightarrow \mathrm{V} & =-2 \times 10^9 \times \frac{\left(-0.8 \times 10^{-6}\right)}{4 \times 10^5} \\ & =4 \times 10^{-3} \mathrm{~m}^3=4 \text { litre } \end{aligned}$$