The number of Glucose molecules present in 10 ml of decimolar solution is

Glucose $\left({\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6\right)$decimolar means 0.1M

V=100ml

Then $\mathrm{M}=\frac{\mathrm{n}\times 1000}{\mathrm{V}\left(\mathrm{ml}\right)}$

$0.1=\frac{\mathrm{n}\times 1000}{10}$

$\mathrm{n}=\frac{0.1}{100}\Rightarrow 0.001$

1mole of glucose contains $6.023\times {10}^{23}$ molecules 

But 0.001mole of glucose contains

$=\frac{6.023\times {10}^{23}}{1}\times 0.001$

$=6.023\times {10}^{23}\times {10}^{-3}$

$=6.023\times {10}^{20} \mathrm{molecules}$