For a closed system-
A(s)⇌2B(g)+3C(g)
Kp=(PB)2×(PC)3
⇒Kp(PC)3=(PB)2 ....(1)
Since, Kp is constant, thus if the partial pressure of C is doubled then P c′=2Pc.
∴Kp=(P′B)2×(P′C)3
Kp=(P′B)2×(2PC)3
⇒Kp(PC)3=8×(P′B)2 ...(2)
From eqn (1) and (2), we have
8×(P′B)2=(PB)2
⇒(P′B)2=18×(PB)2
⇒P′B=12√2×PB
Hence, if the partial pressure of C is doubled then partial pressure of B will be 12√2 times its original pressure.
Hence, x=1 and y=2, x+y=2+1=3.