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# What is the percentage composition of $CaB{{r}_{2}}$? (Atomic weight: Ca = 40, Br = 80)(A) $10%Cr\text{ and 90 }\!\!%\!\!\text{ Br}$ (B) $20%\text{Ca and 80 }\!\!%\!\!\text{ Br}$ (C) $25%\text{Ca and 75 }\!\!%\!\!\text{ Br}$ (D) $33%Ca\text{ and 67 }\!\!%\!\!\text{ Br}$ (E) $50%\text{Ca and 50 }\!\!%\!\!\text{ Br}$

Last updated date: 16th Sep 2024
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Hint: To calculate percentage composition, we must first find the mass/ weight of each atom present and then total weight of the molecules in the given compound. Apply these values in the percentage composition formula:
$%{{C}_{E}}=\dfrac{{{g}_{E}}}{{{g}_{T}}}\times 100$

Complete step by step solution:
The percentage composition of a compound is the ratio of the amount of each element to the total amount of all the elements present in the compound multiplied by 100.
The percentage composition of given element is expressed using the following formula
$%{{C}_{E}}=\dfrac{{{g}_{E}}}{{{g}_{T}}}\times 100$

- Here $%{{C}_{E}}$ gives the percentage composition of the given element E, which is to be calculated.
${{g}_{E}}$, gives the total amount of the element that is present in the given compound.
${{g}_{T}}$, gives the total amount of all the elements present in the compound.
This $\dfrac{{{g}_{E}}}{{{g}_{T}}}$ is further multiplied by 100.

- The given compound is $CaB{{r}_{2}}$.
Relative atomic mass of $Ca$ in $CaB{{r}_{2}}$= 40
Relative atomic mass of $Br$ in $CaB{{r}_{2}}$ = 80
Total molecular mass of the $CaB{{r}_{2}}$ compound = $40\times 1+80\times 2$ $=200g$
% composition of $Ca$$=\dfrac{40}{200}\times 100 = 20%Ca % composition of Br$$=\dfrac{80}{200}\times 100 = 80%Br$
So, the correct answer is “Option B”.