Density of `1M` solution of a non-electrolyte `C_(6)H_(12)O_(6)` is `1.18g//mL`. If `K_(f)(H_(2)O)` is `1.86^(@)kg`, solution freezes at :

Options

A. `-1.58^(@)C`
B. `-1.86^(@)C`
C. `-3.16^(@)C`
D. `1.86^(@)C`

Answer

B

Explanation

`1MC_(6)H_(12)O_(6)`(molar mass `=180g "mol"^(-1)`)
`1000mL` solution has `=180g` solute
`1180g` solution has `=180g` solute
`1000g` solvent has `=180g` solute
Thus, molality`=1` molal
`therefore DeltaT_(f)=K_(f)` molality `=1.86xx1=1.86^(@)`
`therefore F.P.=-1.86^(@)C`