# What is the concentration of chloride ions in a solution whose concentration is 6xx10^-3*mol*L^-1 with respect to "calcium chloride"?

$1.2 \times {10}^{-} 2$ $m o l \cdot {L}^{-} 1$ in chloride ion.
You have quoted a solution of $C a C {l}_{2}$ that is $6 \times {10}^{-} 3$ $m o l \cdot {L}^{-} 1$, and I assume this to be this concentration with respect to the compound itself (i.e. $\left[C a C {l}_{2}\right]$ $=$ $6.0 \times {10}^{- 3}$ $m o l \cdot {L}^{-} 1$ this is typically understood!).
Because this a $C a C {l}_{2}$ solution, for each $C {a}^{2 +}$, there are $2$ equiv $C {l}^{-}$ ion. Chloride ion concentration is effectively doubled to give $1.2 \times {10}^{-} 2$ $m o l \cdot {L}^{-} 1$.