${\mathrm{Co}}^{2+}+\mathrm{KCN}$ (not in excess)$\to$ Precipitate.

Select the correct statement(s) with respect to the precipitate.

so, above equation shows that Precipitate is reddish-brown in colour. It dissolves in excess of the reagent forming a brown solution. It is also obtained when brown solution is acidified with dilute HCl in the cold.

Thus, options is B, C and D are correct.