1. **Problem statement:** Calculate the number of moles in 250 mL of a 2 M (molar) solution. 2. **Formula used:** Molarity (M) is defined as moles of solute per liter of solution: $$ M = \frac{\text{moles}}{\text{liters}} $$ 3. **Rearranging the formula to find moles:** $$ \text{moles} = M \times \text{liters} $$ 4. **Convert volume from mL to liters:** $$ 250 \text{ mL} = \frac{250}{1000} = 0.25 \text{ L} $$ 5. **Calculate moles:** $$ \text{moles} = 2 \text{ M} \times 0.25 \text{ L} = 0.5 \text{ moles} $$ **Final answer:** There are 0.5 moles in 250 mL of a 2 M solution.