Aqueous NaOH solution is labelled as 10% by weight. Mole fraction of the solute in the solution is

w/w% of aq. NaOH =10%

   W_NaOH =10g , W_solution. =100g

     W_water=(100-10) = 90g

${\mathrm{X}}_{\mathrm{NaOH}}=\frac{{\mathrm{n}}_{\mathrm{NaOH}}}{{\mathrm{n}}_{{\mathrm{H}}_2\mathrm{O}}+{\mathrm{n}}_{\mathrm{NaOH}}}$

${\mathrm{X}}_{\mathrm{NaOH}}=\frac{\left(\frac{10}{40}\right)}{\left(\frac{90}{18}\right)+\left(\frac{10}{40}\right)}$

${\mathrm{X}}_{\mathrm{NaOH}}=\frac{1}{21}=0.0476$