calculate the volume (in ml) of 2.25 M HNO3 solution required to react with 24.2 ml of 3.50 M NaOH solution?

NaOH + HNO₃ → NaNO₃ + H₂O
Mole ratio  NaOH : HNO₃ = 1 : 1

Millimoles of NaOH reacted = (3.50 mmol/mL) × (24.2 mL) = 84.7 mmol
Millimoles of HNO₃ required = 84.7 mmol
Volume of HNO₃ required = (84.7 mmol) / (2.25 mmol/mL) = 37.6 mL

====

OR:

(3.5 mol NaOH / 1000 mL NaOH solution) × (24.2 mL NaOH solution) × (1 mol HNO₃ / 1 mol NaOH) × (1000 mL HNO₃ solution / 2.25 mol HNO₃)
= 37.6 mL HNO₃ solution