Cost per mole
Table salt : Rs 0.878
Table sugar : Rs 23.63
<h3>Further explanation</h3>
Given
Cost table salt (NaCl) = 15/kg
Cost table sugar(sucrose-C12H22O11) = 69/kg
Required
cost per mole
Solution
mol of 1 kg Table salt(NaCl ,MW= 58.5 g/mol) :

mol of 1 kg Table sugar(C12H22O11 ,MW= 342 g/mol) :

Answer
Naphthalene is a non electrolyte
If the unknown compound is an electrolyte it gives 2 or more ions in solution
( NaCl >> Na+ + Cl- => 2 ions
Ca(NO3)2 >> Ca2+ + 2 NO3- => 3 ions)
the f.p. lowering is directly proportional to the molal concentration of dissolved ions in the solution )
For naphthalene
delta T = 1.86 x m
for a salt that gives 2 ions
delta T = 1.86 x m x 2
hence the lowering in freezion point of unkown is greater then napthalene