Here's how to calculate the molarity of the potassium chloride (KCl) solution:

1. Convert grams of KCl to moles:

* Molar mass of KCl:

* K: 39.10 g/mol

* Cl: 35.45 g/mol

* Total: 39.10 + 35.45 = 74.55 g/mol

* Moles of KCl:

* (85.0 g KCl) / (74.55 g/mol KCl) = 1.14 mol KCl

2. Convert volume to liters:

* Volume in liters: (400.0 mL) / (1000 mL/L) = 0.400 L

3. Calculate molarity:

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

* M = (1.14 mol KCl) / (0.400 L)

* M = 2.85 M

Therefore, the molarity of the potassium chloride solution is 2.85 M.