And K_a=([H_3O^+][A^-])/([HA])
If K_a is LARGE, then we gots a strong acid...if K_a is small, then we got a weak acid, and the equilibrium LIES to the LEFT as written.
For a. we gots a diprotic acid.....
H_3PO_4(aq) + 2H_2O(l) rightleftharpoonsHPO_4^(-) +2H_3O^+
K_a=([HPO_4^(2-)][H_3O^+]^2)/([H_3PO_4])
For b. we gots a monoprotic weak acid.....
HClO_2(aq) + H_2O(l) rightleftharpoonsClO_2^(-) +H_3O^+
K_a=([HClO_2^(-)][H_3O^+])/([HClO_2])
For c. we gots a monoprotic weak acid.....
HOAc(aq) + H_2O(l) rightleftharpoonsAcO^(-) +H_3O^+
K_a=??. Have bash at the remaining expressions yourself.