[tashkent]

Hello everyone!

I am preparing for my GRE Chemistry exam and I am having problems in figuring out the solution to this GRE problem:

3) In which of the following reactions is the equilibrium farthest to the LEFT?

a)   P4O10 + x H2O = 4H3PO4
b)   AlCl3 + xH2O = [Al(H2O)6]+3 + 3Cl-
c)   Li2O + xH2O = 2Li+(aq) + 2OH-(aq)
d)   H2S + H2O = H3O+ + HS-(aq)
e)   CaC2 + xH2O = Ca+2(aq) + 2OH-(aq) + C2H2(g)

The answer is letter D, but I can't figure out why.  Hope to receive ideas from kind souls here...

I will appreciate your responses.  Thanks very much.

Sincerely,
Tashkent

[AWK]

H2S is a weak acid and dissociate only in a few percents or less (it depends on concentration)