Chlorophyll extracted from the crushed green leaves was dissolved...

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.

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

$⇒ {W}_{Mg} = \dfrac{48 \times 2 \times 1000}{{10}^{6}}$

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

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

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

Number of $Mg$ atoms $= 4 \times {10}^{- 3} \times 6 . 02 \times {10}^{23} = 4 \times 6 . 02 \times {10}^{20}$

$= 4 \times 6 . 02 \times {10}^{20}$

$= 24 . 08 \times {10}^{20}$

$∴ x = 24 . 08$