Coordination number of $\mathrm{Co}$ in ${\left[{\mathrm{CoF}}_6\right]}^{-3}$ is:

Which of the following compound is expected to yield a white precipitate with ${\mathrm{AgNO}}_3$ solution :
(a) ${\mathrm{PtCl}}_4·4{\mathrm{NH}}_3$
(b) ${\mathrm{CoCl}}_3·3{\mathrm{NH}}_3$
(c) Impure chloroform
(d) Vinyl chloride
(e)

(f) Carnallite