The reaction a(g)⇌2b(g) has an equilibrium constant of k = 0.030. what is the equilibrium constant for the reaction b(g)⇌12a(g)?

First, we have to correct the equation in the question to b(g)⇆ 1/2 A(g)
at the first equation A(g)⇆ 2 B(g) so,
 Kc = [B]^2 [ A] = 0.03 

by reverse the equation 2B⇆ A 
∴ Kc(original) = [A] / [B]^2

        = 1/0.03 = 33 M^-1

and the new equation B⇆ (1/2) A 
So, the new Kc = √Kc(original = √33 
                ∴    KC  = 5.7

Mg-26 and mg-24 are pair of isotopes. isotopes are defined as atoms of the same element having same atomic number but different mass number. i hope that was .