If 0.50 L of a 5.00 M stock solution of HCL is diluted to make 2.0 L of solution, how much HCL, in grams, is in the solution?

The number of moles does not change when you dilute a solution. if you find the moles in the original solution, should be the same amount of moles in the diluted solution.

mole HCl = (0.50 L) x (5.00M) = 2.50 moles HCl

use the molar mass to change moles to grams

2.50 mole HCl (36.51 grams / 1 mole) = 91.3 grams HCl