Question

Chlorophyll, the green colouring matter of plants responsible for photosynthesis contains 2.68 % of magnesium by mass. The number of magnesium atoms in 2.00 g of chlorophyll are

• A. $1.33\times 10^{23}$
• B. $6.02\times 10^{23}$
• C. $3.01\times 10^{21}$
• D. $1.34\times 10^{21}$

Answer 1

Answer: (D)

Mass of magnesium $=\frac{2.00g\times 2.68}{100}$
$=5.36\times 10^{-2}g$
$24g$ of $Mg=6.02\times 10^{23}$ atoms
$\therefore 5.36\times 10^{-2}g$ of $Mg$
$=\frac{(6.02\times 10^{23}atoms)\times (5.36\times 10^{-2}g)}{24g}$
$=1.34\times 10^{21}$ atoms