Question

The formula of oxide of potassium with percentage of oxygen being $45.07\%$ is:
A.${{\text{K}}_{\text{2}}}{\text{O}}$
B.${\text{K}}{{\text{O}}_{\text{2}}}$
C.${{\text{K}}_{\text{2}}}{{\text{O}}_{\text{2}}}$
D.None of these

Answer 1

Percentage of an element in the compound is calculated as the ratio of mass of that element in the compound to the total mass of the compound multiplied by $100$. Total mass of the compound is calculated as the sum of the masses of all elements present in the compound.

Complete step by step answer:
First of all let us read about molecular formulas.
Molecular weight of the substance: It is defined as the sum of the molecular masses of all elements present in the substance.
Number of moles: It is defined as the ratio of mass of the substance to the molecular mass of the substance.
Molecular formula: The molecular composition in the compound is known as molecular formula. For example: the molecule of water is ${H_2}O$ i.e. two atoms of hydrogen with oxygen.
Here in the question we are given the compound of potassium and oxygen and also we know the molecular weight of potassium which is $39$ and molecular weight of oxygen is $16$. In the question we are given with the percentage of oxygen as $45.07\%$.
In option A) ${{\text{K}}_{\text{2}}}{\text{O}}$ the percentage of oxygen is as $\dfrac{{16}}{{94}} \times 100 = 17.02\%$, where $16$ is the molecular weight of oxygen and $94$ is the molecular weight of ${K_2}O$.
In option B) ${\text{K}}{{\text{O}}_2}$ the percentage of oxygen is as $\dfrac{{32}}{{71}} \times 100 = 45.07\%$, where $32$ is the molecular weight of oxygen and $71$ is the molecular weight of $K{O_2}$.
In option C) ${K_2}{O_2}$ the percentage of oxygen is as $\dfrac{{32}}{{110}} \times 100 = 29.09\%$, where $32$ is the molecular weight of oxygen and $110$ is the molecular weight of ${K_2}{O_2}$.

So option B is correct i.e. $K{O_2}$. Hence the formula of oxide of potassium with percentage of oxygen being $45.07\%$ is $K{O_2}$.

Additional information:
Atoms: It is the smallest unit of an element. The elements are made of the same kind of atoms. In the atoms there are three particles: electrons, protons and neutrons.
Electrons: They are the negatively charged particle having negligible mass. They move in the atoms outside the nucleus in a fixed orbit.
Protons: They are positively charged particles. They have mass. They are present in the nucleus (a special room in the atoms were neutrons and protons are present).
Neutrons: They have no charge but they have mass. They are also present in the nucleus along with protons.
Gram molecule: It is defined as the number of grams of the substance i.e. the molecular mass of the substance.
Atomic mass: It is defined as the total number of protons and neutrons present in the nucleus of an atom. It is represented by symbol A.
Atomic number: It is defined as the number of protons in the nucleus of an atom. It is represented by symbol Z.

Note:
Formula mass: It is defined as the sum of the atomic weights of all the atoms present in the compound. And if the compound is covalent in nature then the formula mass is known as molecular mass and if we are calculating mass of one mole of substance then it is known as molar mass.