Asample of gas in which [h2s] = 5.76 m is heated to 1400 k in a sealed vessel. after chemical equilibrium has been achieved, what is the value of [h2s]? assume no h2 or s2 was present in the original sample.

According to the equation reaction:
                      2H2S(g) ↔ 2H2(g) + S2(g)
initial m        5.76m             0            0
change          -X                  +X           +X
final            (5.76-X)             X             X 

and when we have Kc = 2.2x10^-4 (given) so, by substitution:

Kc = [H2]^2*[S2]/[H2S]^2
2.2x10^-4 =( X^2*X)/(5.76-X)

∴X= 0.11 m
∴[H2S] = 5.76 - X = 5.76 - 0.11 = 5.65 m

The answer is a) carbon-12