In which of the following reactions, the concentration of reactant is equal to concentration of product at equilibrium ( $\mathrm{K}=$ equilibrium constant)?
(a) $\mathrm{A} \rightleftharpoons \mathrm{B} ; \mathrm{K}=0.01$
(b) $\mathrm{R} \rightleftharpoons \mathrm{P} ; \mathrm{K}=1$
(c) $\mathrm{X} \rightleftharpoons \mathrm{Y}$; $\mathrm{K}=10$
(d) $\mathrm{L} \rightleftharpoons \mathrm{J} ;=0.025$