What are the variables physical change vs chemical change

Which of these conditions most likely produces an unstable isotope?

Word equation for k(s)+h2o(l) yield koh(aq) + h2(g)

Amixture initially contains a, b, and c in the following concentrations: [a] = 0.300 m , [b] = 1.05 m , and [c] = 0.550 m . the following reaction occurs and equilibrium is established: a+2b⇌c at equilibrium, [a] = 0.140 m and [c] = 0.710 m . calculate the value of the equilibrium constant, kc.