Molar mass of C2H4O2: 12 × 2 + 1 × 4 + 16 × 2 = 60 g mol–1
Moles of C2H4O2 = 
1
2 5 g
60 g mol−  =  0 0417 mol
Mass of benzene in kg = 75 g/1000 g kg–1 = 75 × 10–3 kg
Molality of C2H4O2 = 
2
4
2
Moles of C H O
kg of benzene
 = 
1
0 0417 mol
1000 g kg
 
75 g 
−
×
                            = 0