In the complex, ${\mathrm{CoCl}}_3. 5{\mathrm{NH}}_3$, the primary valency of the central metal is satisfied by

According to Werner's theory, primary valency of a metal is satisfied by negative ions only.

Werner formula …${\mathrm{CoCl}}_3. 5{\mathrm{NH}}_3$

Modern formula . . .$\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5{\mathrm{Cl}}_{ }\right]{\mathrm{Cl}}_2$

One chloride ion satisfies both primary and secondary valency. 

Two chloride ions satisfy primary valency only. 

Five ammonia molecules satisfy secondary valency only.