Answer
0.507 atm
Work Step by Step
Volume $V=560 \,mL=0.560\,L$
Number of moles $n=\frac{1.55\,g}{131.293\,g/mol}=0.0118\,mol$
Universal gas constant $R= 0.0821\,L\,atm\,mol^{-1}K^{-1}$
Temperature $T=(20 \,+273)K= 293\,K$
Recall that $PV=nRT$ (ideal gas law)
$\implies $ Pressure $P= \frac{nRT}{V}$
$=\frac{(0.0118\,mol)(0.0821\,L\,atm\,mol^{-1}K^{-1})(293\,K)}{0.560\,L}$
$=0.507\,atm$
