At constant temperature & volume, 50% of ozone is decomposed out of 2 atm of ozone taken initially and the equilibrium  is established, Kp for the decomposition of ozone is

Initial pressure of O3 = 2 atmdegree of decomposition =Decrease in pressure due to decomposition of O3 = 0.5 x 2= 1 atm2 moles of O3 → 3 moles of O21 moles of O3 → 'x' moles of O2Number of molesα  partial pressure