Given
Urea (A), WA= ?
MA= 60g/mol
Water (B), WB = 100g
MB = 18g/mol
P° = 31.80mm
P°- Ps = 0.25mm
Now,
P° - Ps /P° = WA /MA× MB / WB
0.25/31.80= WA /60× 18 /100
0.25/31.80= WA/30 × 9/100
WA = 0.25×30× 100/31.80× 9
= 0.25× 10 × 100/31.80× 3
= 250/31.8 ×3
= 2500/954
WA = 26.2 g