∵NaCl is an ionic salt and go for complete ionisation, so has maximum osmotic pressure, while glucose and urea does not ionises. For NaCl(i=2) and for glucose and urea (i=1) ∵π=iCRT where, π= osmotic pressure i= van't Hoff factor C= molarity R= gas constant T= temperature in Kelvin Also, π=i
n
V
RT[∵C=
n
V
] and π=i
w
M×V
RT If V,R and T are same π∝i×
w
M
where, n= number of moles of solute w= mass of solute M= molar mass of solute V= volume Thus, (i) 30gmL−1 of glucose (w=30,M=180) π∝
1×30
180
=0.166 (ii) 60gmL−1 of NH2CONH2 (w=60,M=60) π∝
1×60
60
=1.00 (iii) 80gmL−1 of glucose (w=80,M=180) π∝
1×80
80
=0.44 (iv) 58.5gmL−1 of NaCl (i=2)w=58.5,M=58.5 ∴π∝i
w
M
=2×
58.5
58.5
=2 Hence, order of osmotic pressure will be (i) <(iii)<(ii)<(iv)