Answer: 0.471 (3s.f)
Step-by-step explanation:
Let x moles of HI being formed.
[H2]=0.3-2x
[I2]=0.3-x
Kc=[HI]^2/[I2][H2]
53.3=x^2/(0.3-x/2)(0.3-x/2)
53.3(0.3-0.5x)^2=x^2
When solved for we get,
x=0.47098
Concentration of HI present is therefore 0.47098.
Or 0.471 (3 significant figures).