A solution is prepared by mixing 100 mL of 1 M HCl and 250 mL of 5 M NaCl. What is the total volume of the solution?

350 mL

Explanation:

Normally, in the neutralization reactions, that is how the reactions between and acid and a base are called, you assume additive volumes.

Additive volumes means that the volume of the final solution is equal to the sum of the separate volumes of the two solutions that are mixed.

It is not totally accurate, but it is a good approximation and for lack of additional data it is what is used.

Then, assuming additive volumes:

Total volume of the solution = 100 mL + 250 mL = 350 mL.