Answer
-33° C
Work Step by Step
$P_{1}=1.80\,atm$
$V_{1}=124\,mL$
$T_{1}= (212+273)K= 485\,K$
$P_{2}= 0.800\,atm$
$V_{2}=138\,mL$
Combined gas law is
$\frac{P_{1}V_{1}}{T_{1}}=\frac{P_{2}V_{2}}{T_{2}}$ (if n is constant)
$\implies T_{2}=\frac{P_{2}V_{2}T_{1}}{P_{1}V_{1}}$
$=\frac{0.800\,atm\times138\,mL\times485\,K}{1.80\,atm\times124\,mL}=240.\,K$
$=(240-273)^{\circ}C=-33^{\circ}C$
