Answer will be 0.75 atm .
According to gas law given by Gay lussac-
"pressure of a gas is directly proportional to the temperature(kelvins) of the gas when volume is kept constant".
[tex]\frac{P_1}{T_1}=\frac{P_2}{T_2}[/tex]
given:
[tex]P_{1}=0.82 atm[/tex]
[tex]T_{1}=21^{\circ}C=21+273.15K=294.15K[/tex]
[tex]P_{2}=?[/tex]
[tex]T_{2}=-3.5^{\circ}C=-3.5+273.15K=269.65K[/tex]
Now putting the respective values is the equation (1)
[tex]\frac{P_1}{T_1}=\frac{P_2}{T_2}[/tex]
[tex]\frac{0.82}{294.15}=\frac{P_2}{269.65}[/tex]
[tex]P_{2} = 0.75 atm[/tex]
