Question -
Answer -
Molar mass of urea (NH2CONH2) = 2(1 × 14 + 2 × 1) + 1 × 12 + 1 × 16
= 60 g mol−1
0.25 molar aqueous solution of urea means:
1000 g ofwater contains 0.25 mol = (0.25 × 60)g of urea
= 15 g ofurea
That is,
(1000 + 15) g of solution contains 15 g of urea
Therefore,2.5 kg (2500 g) of solution contains 
= 36.95 g
= 37 g of urea (approximately)
Hence, mass of urea required = 37g