w=2g M of NaOH=40 V of solution 200‌mL ‌‌ Molarity ‌=‌
w
M
×‌
1000
V(mL)
‌‌=‌
2
40
×‌
1000
200
=0.25 at 25° C But as temperature increases, water expands, ∴ The volume of solution increases. Hence at 90∘C the molarity will be less than 0.25.