$\begin{array}{1 1}(a)\;6.02\times 10^{20}& (b)\; 6.02\times 10^{19}\\(c)\;1.2\times 10^{20}& (d)\;1.2\times 10^{22}\end{array} $

Molarity of NaCl=$\large\frac{5.85}{58.5}$$\times 10^{-1}$

$\therefore$ 1ml of NaCl=$10^{-4}$mol

1 mol of NaCl=$6.023\times 10^{23}$ molecules of NaCl .But NaCl molecules are dissociated into two ions $(Na^+$ and $Cl^{-})$

$\therefore$ 1mol of NaCl =$6.023\times 10^{23}\times 2$ions.

$\therefore 1\times 10^{-4}$mole of NaCl =$6.023\times 10^{23}\times 2$ions.

$\Rightarrow 1.2\times 10^{20}$ions

Hence (c) $1.2\times 10^{20}$ions is the correct answer.

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