Question

a balloon has 175ml at 1.00 bar.calculate it's volume at 0.80 atm if temperature is constant.

Answer 1

1 bar is approximately equal to 1 atm.

At Const. Temp.
$P_{1}V_{1}=P_{2}V_{2}$
$V_{2}= P_{1}V_{1}/P_{2}$ = 175 × 1/0.8 = 218.75mL
      

Answer 2

V1=175,p1=1bar,v2=?p2=0.80atm Therefore, By Boyle's law, P1v1=p2v2 =p1v1/p2 =1*175/0.80 =218.75L