Answer
Please see the work below.
Work Step by Step
We know that
$n=\frac{PV}{RT}$
$n=\frac{\frac{72}{760}\times 0.1250}{0.08206(17+273)}=0.004990\space mol$
$0.2040\frac{mol}{L}\times 0.04990L=0.0099756mol\space acid$
The acid is $HCl$ because the ratio of acid to $CO_2$ is
$\frac{0.0099756}{0.004990}=2.00$
