Here's how to calculate the molarity of a KCl solution:

1. Convert grams of KCl to moles:

* Find the molar mass of KCl: K (39.10 g/mol) + Cl (35.45 g/mol) = 74.55 g/mol

* Divide the mass of KCl by its molar mass: 140 g / 74.55 g/mol = 1.87 mol KCl

2. Convert milliliters of water to liters:

* Divide the volume by 1000: 600 mL / 1000 mL/L = 0.600 L

3. Calculate molarity:

* Molarity (M) = moles of solute / liters of solution

* M = 1.87 mol KCl / 0.600 L = 3.12 M

Therefore, the molarity of the KCl solution is 3.12 M.