Answer :
The equilibrium will be
[tex]NaHCO_{3} (s)--->Na_{2} CO_{3} (s)+CO_{2} (g)+H_{2}O(g)[/tex]
There is no gas in the reactant
The Kp expression for equilibrium will be
Kp = pH₂O X pCO₂
Given Kp =0.23
thus
0.23= pH₂O X pCO₂
The partial pressures of both will be equal, lets say "p"
0.23=p²
p=0.48
Total pressure = 0.48 + 0.48 = 0.96 atm
Answer is 0.96 atm