Answer:
19.07 atm 
Step-by-step explanation:
Data obtained from the question include the following:
Number of mole (n) = 0.9 mole
Temperature (T) = 50°C = 50°C + 273 = 323K 
Volume (V) = 1.25L
Pressure (P) =...? 
Note: the gas constant (R) = 0.082atm.L/Kmol 
The pressure exerted by the gas can be obtained by using the ideal gas equation as illustrated below:
PV = nRT 
P = nRT /V 
P= (0.9 x 0.082 x 323)/1.25
P = 19.07 atm 
Therefore, the pressure exerted by the gas is 19.07 atm