$\left[{Cr}\left({H}_{2} {O}\right)_{3}\left({NH}_{3}\right)_{3}\right] {Cl}_{3} \rightarrow\left[{Cr}\left({H}_{2} {O}\right)_{3}\left({NH}_{3}\right)_{3}\right]^{3+}+3 {Cl}^{-} \overset{AgNO_3}{\rightarrow} AgCl$

$1\, mole$ $\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad1\, mole$ $\quad\quad\quad\quad3\, mole \quad\quad\quad3\, mole$

Since none of ${Cl}^{-}$is present in the co-ordination sphere. Therefore answer is zero.