A `5%` solution of cane sugar (molecular weight =`342`) is isotonic with a `1%` solution of substance `X`. The molecular weight of `X` is

Options

A. `34.2`
B. `171.2`
C. `68.4`
D. `136.8`

Answer

C

Explanation

Isotonic solutions are the solutions having same osmotic pressure.
Osmotic pressure of 5% cane sugar solution
`(pi_(1))=C xx R xx T`
`=(50g//L)/(342)xx0.0821xx T`
Osmotic pressure of 1% solution of substance
`X (pi_(2))=(10g//L)/(M)xx0.0821xx T`
Both are isotonic
So, `pi_(1)=pi_(2)`
or `(50)/(342)xx0.0821xx T(10)/(M)xx0.0821xx T`
`therefore M("molecular weight of X")=(342)/(5)=68.4`