A balloon contains 1500   m 3 of He at 27 ° C and 4 atmospheric pressure. the volume of He at - 3…

The quantity of gas is same in both situations, therefore using the ideal gas equation, $PV=nRT$here, $n$is the number of moles of gas and $R$is the universal gas constant.

when pressure is $P_1=4 \mathrm{atm}$ and temperature is $T_1=27°\mathrm{C}=300 \mathrm{K}$then volume is $V_1=1500 {\mathrm{m}}^3$ 

$$\begin{gathered} \Rightarrow \frac{P_1{V}_1}{T_1}=\frac{P_2{V}_2}{T_2} \\ \Rightarrow \frac{1500\times 4}{300}=\frac{V_2\times 2}{270} \\ \Rightarrow V_2=2700 {\mathrm{m}}^3 \end{gathered}$$