How many of the following compounds produce a product having molecular weight equal to heavy water ( $D_{2}O$ ) when dissolved in heavy water.

${\mathrm{CaC}}_2,{\mathrm{Mg}}_3{\mathrm{N}}_2,{\mathrm{Be}}_2\mathrm{C},{\mathrm{Al}}_4{\mathrm{C}}_3,{\mathrm{Ca}}_3{\mathrm{P}}_2,\mathrm{HCl}$