Decomposition of  non volatile solute (A)  into  another  non  volatile  solute  B and C.When dissolved in water follows  first order kinetics as
A(s)    ^H2O------  2B(s) + C(s)
If initially  two moles  of A is  dissolved in 360g of H₂O and left for decomposition at  constant temperature (25 deg)  Then  P_S  in the  given table is ( assuming A,B and C are  miscible in water)
S.N.        Time                  The vapour pressure  of solution
1.           12 hr                                20mm Hg
2 .           80hr                                P_S
Vapour pressure  of H₂O at 25 deg is 24mm Hg(Log2 = 0.30)