Balloons of 4 litre capacity are to be filled with hydrogen gas at a pressure of 1 atm and 27°C from an 8 litre cylinder containing hydrogen at 10 atm at the same temperature.  The number of balloons that can be filled are ____?

$\begin{array}{l}{P}_1{V}_1=P_2{V}_2\\ 10\times 8=1\times V_2\\ V_2=80 \mathrm{lit}re\end{array}$

$\therefore \text{ Vol of hydrogen gas that can be filled in balloons }=V_2-V_1$

                                                                                                                           =  80 – 8 =  72

$\therefore \text{ No. of balloons can be filled }=\frac{72}{4}=18$