A volume of 50.00 mL of a weak acid of unknown concentration is titrated with 0.10 M solution of NaOH. The equivalence point is reached after 39.30 mL of NaOH solution has been added. At the half equivalence point (19.65 mL) the pH is 4.85. Thus, initial concentration of the acid and its pK_a values are

A(g) $$\to$$ P(g) + Q(g) + R(g),

Follow first order kinetics with a half-life of 69.3 s at 500$$^\circ$$C. Starting from the gas 'A' an container at 500$$^\circ$$C and at a pressure of 0.4 atm, the total pressure of the system after 230 s will be