Question

The simplest formula of a compound containing $50\%$ of an element $X$ (Atomic weight
$10$ ) and $50\%$ of an element $Y$(Atomic weight $20$ ) is:
A. $XY$
B. ${X_2}Y$
C. $X{Y_2}$
D. ${X_2}{Y_3}$

Answer 1

The chemical formula of a chemical compound is estimated by determining the number of moles of the individual elements in the chemical compound, such that, on decomposition, their stoichiometry is easily explained without any ambiguity.

Complete step by step answer:
In the given question, it has been mentioned that the compound consists of two elements $X$ and $Y$ . The corresponding atomic masses of $X$ and $Y$ are $10$ and $20$, respectively. In order to calculate the number of moles of both the elements, we must specify some constant weight of the elements.
Let the weight of the compound taken be $100g$.
As it is mentioned in the question, the mass percentage of both the elements in the compound are found to be the same and equal to $50\%$ each. Thus, according to this:
Weight of $X$ taken = $50g$
Weight of $Y$ taken = $50g$
The number of moles of any substance is the ratio of the given weight of the element and the atomic weight of that element.
Hence, number of moles of $X$ = $\dfrac{{50}}{{10}} = 5$
Similarly, number of moles of $Y$= $\dfrac{{50}}{{20}} = 2.5$
Thus, the compound can be written as ${X_5}{Y_{2.5}}$. In simpler terms, the chemical formula of the compound can be written as ${X_2}Y$.
The correct option is B. ${X_2}Y$.

Note:
The chemical formula of any compound is determined simply by estimating the stoichiometric coefficients of the individual elements in the compound. This can also be determined by the valency exchange method but for that, the electronic configuration of the elements should be known.