Given, half-life = 69.3 s
Half-life for first order reaction
k=‌=‌=10−2s−1 For first order kinetics,
k=‌‌log‌ 10−2=‌‌log‌ log‌=1 log‌10=log‌  (as log 10 = 1)
10=‌ pt=‌=0.04 From the reaction,
      A(g) → P(g) + Q(g) + R(g)
At
t=0   0.4  0   0  0
At
t=230s 0.04 0.4 - x 0.4-x 0.4-x
Now, at time t = 230 s, the pressure of the gases
=0.04+0.36+0.36+0.36=1.12
atm