When 200. ml of water are added to 100. ml of 12% kcl solution the final concentration of kcl is (assume the volumes add.) ?

Since the original concentration is expressed in terms of mass %, let's also answer with mass %. To do this easily, let's use the formula for mass dilution.

C₁V₁ = C₂V₂

where C stands for concentration and V stands for volume

The solution is as follows:

(12%) (100 mL) = (C₂) (100 mL + 200 mL)

Solving for C₂,

C₂ = 4%