If a solution contains 0.02 mol solute in 1 L, find molarity.

Molarity for 0.02 mol solute in 1 L
Answer: $M=\dfrac{0.02}{1.00}=0.020\ \text{mol L}^{-1}$.
Method: Straight definition. If the final volume were different after mixing, use the final solution volume. For serial dilutions, $M_1V_1=M_2V_2$ helps compute volumes required to reach 0.020 M from a stock. Units should always be reported to three significant figures if data warrant.