Chlorophyll is the green pigment in plants, algae, and cyanobacteria that is essential for photosynthesis. Its central structure is an aromatic porphyrin ring system with a sequestered magnesium atom.

$\mathrm{ppm}=\frac{{\mathrm{W}}_{{\mathrm{M}}_{\mathrm{g}}}}{{\mathrm{V}}_{\mathrm{sol}}}\times {10}^6=48$

$\Rightarrow {\mathrm{W}}_{\mathrm{Mg}}=\frac{48\times 2\times 1000}{{10}^6}$

$=48\times 2\times {10}^{-3} \mathrm{g}$

${\mathrm{n}}_{\mathrm{Mg}}=\frac{{\mathrm{W}}_{\mathrm{Mg}}}{24}=\frac{48\times 2\times {10}^{-3}}{24}$

$=4\times {10}^{-3}$

Number of $\mathrm{Mg}$ atoms $=4\times {10}^{-3}\times 6.02\times {10}^{23}=4\times 6.02\times {10}^{20}$

$=4\times 6.02\times {10}^{20}$

$=24.08\times {10}^{20}$

$\therefore \mathrm{x}=24.08$