${\mathrm{CaCO}}_{3\left(s\right)}\rightleftharpoons {\mathrm{CaO}}_{is)}+{\mathrm{CO}}_{2\left(\mathrm{g}\right)}$ which of the following 

expression is correct 

Or 

For the equilibrium  ${\mathrm{CaCO}}_{3\left(\mathrm{s}\right)}\rightleftharpoons {\mathrm{CaO}}_{\left(\mathrm{s}\right)}+{\mathrm{CO}}_{2\left(\mathrm{g}\right)}$ the

equilibrium constant is represented by the following form