The number of ions in $2.2\times {10}^{-3}$ moles of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2 \mathrm{are}$

The balanced chemical reaction is, 

$1\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\to 1\underset{⏟3 \mathrm{ions}}{{\mathrm{Ca}}^{+2}+2{\mathrm{OH}}^{-}}$

In one $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ molecule 3 ions will present

1 Mole of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$has Avogadro’s number, $6\times {10}^{23} \mathrm{of} \mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ molecules.

One mole of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ molecules $=3\times 6\times {10}^{23} \mathrm{ions}$

Number of ions present in $2.2\times {10}^{-3} \mathrm{moles} \mathrm{of} \mathrm{Ca}{\left(\mathrm{OH}\right)}_2$

$\frac{2.2\times {10}^{-3}\times 18\times {10}^{23}}{1 \mathrm{mol} \mathrm{Ca}{\left(\mathrm{OH}\right)}_2}=39.6\times {10}^{20 }ions$