Step 1 is to calculate the amount of hydroxyzine HCL in each mL of the oral suspension. This is done by dividing the total amount of hydroxyzine HCL (25 mg) by the total volume (5 mL), which gives us 5 mg/mL. Step 2 is to calculate the volume of oral suspension that contains 50 mg of hydroxyzine HCL. This is done by dividing the prescribed dose (50 mg) by the concentration of the oral suspension (5 mg/mL). So, 50 mg ÷ 5 mg/mL = 10 mL. So, the correct answer is 10 mL.