Question

Two elements $P$(atomic weight$=75$) and $Q$(atomic weight$=16$) combine to give a compound having $75.8$of$P$. The formula of the compound is
A. $XY$
B. ${{X}_{2}}Y$
C. $X{{Y}_{2}}$
D. ${{X}_{2}}{{Y}_{3}}$

Answer 1

To solve this question, we will utilize the method of searching the empirical formula of a compound. In chemistry, the empirical formula of the compound is the simplest positive integer ratio of different atoms present in a compound.

Complete Step by step answer:
Empirical formulas are the simplest form of notation. They give the most reduced whole- number ratio between the elements in a compound. In contrast to molecular formulas, they don't provide information about the quantity of absolute number of atoms in a single molecule of a compound.
Convert the mass of every element to moles utilizing the molar mass from the periodic table. Divide every mole value by the smallest number of moles determined. Round to the closest whole number. This is the mole ratio of the elements and is subscripts in the empirical formula.
Given:
There are two elements in the compound, $X$ and $Y$
Atomic mass of $X=75$
Atomic mass of $Y=16$
Percentage of $X=75.8$
Percentage of $Y=\left( 100-75.8 \right)$
Now, using the empirical formula,

Element	Percentage of element	Atomic mass of element	Relative numbers of atoms	Simplest atom ration	Simplest whole number atom ratio
$X$	$75.8$	$75$	$\dfrac{75.8}{75}=1.01$	$\dfrac{1.01}{1.01}=1$	$1\times 2=2$
$Y$	$24.2$	$16$	$\dfrac{24.2}{16}=1.51$	$\dfrac{1.51}{1.01}=1.5$	$1.5\times 2=3$

Hence, the empirical formula of the compound is ${{X}_{2}}{{Y}_{3}}$

So, the correct option is D.

Note: Molecular formula of a compound is in every case more useful than the empirical formula as the empirical formula can just inform us regarding the relative ration in which the molecules have combined. Yet, the molecular formula reveals to us the specific number of atoms that have combined to shape the compound.