What number of moles of solute are present in 25.0 mL of 2.00 M HCl?

Molarity is defined as the number of moles of solute in 1 L of solution

molarity of given HCl solution is 2.00 M

this means that there are 2.00 mol of HCl solute in 1 L solution

so if 1000 mL contains - 2.00 mol

then 25.0 mL contains - 2.00 mol / 1000 mL/L x 25.0 mL = 0.0500 mol

number of moles of solute are 0.0500 mol