[ઉપયોગ: પરમાણ્વીય દળ:$Na:23.0\,u {O}: 16.0 \,{u} \quad {H}: 1.0 \,{u}$, ઘનતા ${H}_{2} {O}: 1.0 \,{~g} \,{~cm}^{-3}$ ]
mass of solution \(=(1.2 \times 1000)\, {g}\)
\(=1200\, {gm}\)
Neglecting volume of \({NaOH}\)
Mass of water \(=1000\, {gm}\)
\(\Rightarrow\) Mass of \({NaOH}=(1200-1000)\, {gm}\)
\(=200\, {gm}\)
\(\Rightarrow\) Moles of \({NaOH}=\frac{200\, {~g}}{50\, {~g} / {mol}}=5\, {~mol}\)
\(\Rightarrow\) molality \(=\frac{5 \,{~mol}}{1\, {~kg}}=5\, {~m}\)
$( N _{ A }=6.02 \times 10^{23} \,mol ^{-1})$(નજીકનો પૂર્ણાંક)