To determine the molarity of a solution after diluting a chloride solution, we can apply the dilution formula, which is expressed as:

M₁V₁ = M₂V₂

In this scenario, we start with 100 mL of a 0.75 M chloride solution and add 200 mL of pure water. The initial molarity (M₁) is 0.75 M, and the initial volume (V₁) is 100 mL. The final volume (V₂) is the sum of the initial volume and the volume of water added:

V₂ = 100 mL + 200 mL = 300 mL

We need to find the new molarity (M₂). Rearranging the dilution formula to solve for M₂ gives us:

M₂ = (M₁V₁) / V₂

Substituting the known values into the equation:

M₂ = (0.75 M × 100 mL) / 300 mL

Calculating this yields:

M₂ = 75 / 300 = 0.25 M

Thus, the molarity of the diluted solution is 0.25 M. This demonstrates that when diluting a solution, the new concentration (M₂) is always less than the original concentration (M₁), confirming the principles of dilution.