A $0.6\%$ solution of urea (molecular weight $= 60$) would be isotonic with

Isotonic solutions are those which have same Osmotic pressure($\mathrm{\varphi }$).

$\mathrm{\varphi }$ is same when concentrations are same.

${\mathrm{M}}_{\mathrm{urea}}=\frac{0.6}{60}=0.1\mathrm{M}$

Hence Option(2) is correct.