What is the molarity of a solution, made from 10 mL of a 1.00 M solution, and then diluted by adding 90 mL water?

0.10 M

Explanation:

use the dilution equation (Volume 1) (Molarity 1) = (Volume 2) (Molarity 2)

plugging in the numbers. (10 mL) (1.00 M) = (10 mL+90mL) (X M)

solving for X M = (10 mL x 1.00 M) / (100 mL)

gives you 0.10 M solution