Correct Answer - C
`{:(PCl_(5),hArr,PCl_(3),+,Cl_(2)),(1,,0,,0),(1-alpha,,alpha,,alpha):}`
`K_(p) = [(alpha^(2))/(1 - alpha)][(P)/(1 + alpha)]^(1)`
An increase in pressure will decrease `alpha` , to have `K_(p)` constant and thus backward reaction occurs.