In the system ${\mathrm{CaCO}}_3\left(\mathrm{s}\right)\rightleftharpoons \mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$, doubling the mass of CaO will cause the equilibrium concentration of CO₂ to 

become half of its initial value

remain unchanged 

become twice its initial value

a value which cannot be predicted unless K_c is known