• question_answer A wheather balloon filled with hydrogen at 1 atm and ${{27}^{o}}C$ has volume equal to 12000 litres. On ascending it reaches a place where the temperature is $-{{23}^{o}}C$ and pressure is 0.5 atm. The volume of the balloon is [CBSE PMT 1991] A)                 24000 litres          B)                 20000 litres C)                 10000 litres          D)                 12000 litres

${{V}_{2}}=\frac{{{P}_{1}}}{{{P}_{2}}}\frac{{{T}_{2}}}{{{T}_{1}}}.{{V}_{1}}=\frac{1}{0.5}\times \frac{250}{300}\times 12000lit.=20000lit.$