The initial concentrations of Na and Cl− in the reaction below are each 0. 0517 M. If the initial concentration of NaCl is 0 M and the equilibrium constant is Kc = 8. 21 under certain conditions, what is the equilibrium concentration of Na?
NaCl(aq) ⇌ Na(aq) + Cl−(aq)

a) 0. 0517 M
b) 0. 0517/8. 21 M
c) 0. 1034 M
d) 0. 026 M