Answer :
Kc = [HI]² / {[H2] [I2]}
53.3 = (2x)² / {(0.400M - x)(0.400M - x)}
sqrt(53.3) = 2x / (0.400M - x)
2.92 - 7.30x = 2x
x = 0.314M
[HI] = 2x = 0.628M
53.3 = (2x)² / {(0.400M - x)(0.400M - x)}
sqrt(53.3) = 2x / (0.400M - x)
2.92 - 7.30x = 2x
x = 0.314M
[HI] = 2x = 0.628M