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.