Resulting pressure is 13.6 atm.
Step-by-step explanation:
Using Ideal gas equation, we can find the pressure of the gases formed in the reaction.
PV = nRT
Number of moles, n = given mass / molar mass = 20 g / 18 g/mol 
 = 1.11 moles
Volume, V = 2 L 
 Temperature, T = 25°C + 273 = 298 K 
 R = gas constant = 0.08206 L atm K⁻¹ mol⁻¹
P = nRT/V
 = 1.11×0.08206 ×298 / 2 
 = 13.6 atm