A vessel at 1000 K contains CO2 with a pressure of 0.5 atm. Some of CO2 is converted into CO on addtion of graphite. The value of 'K' at equilibrium for the reaction, CO2g+Cs⇌2COg,  when total pressure is 0.8 atm will be

Let the decrease in pressure of CO2 due to its reaction with graphite = x atmPressure of gas α number of moles1 mole of CO2 gives 2 moles of COx atm of CO2 gives _______ of CO PCO (newly formed) - 2x atmTotal pressure at equilibrium = (0.5 - x + 2x) atm= (0.5 + x) atmGiven 0.5 + x = 0.8