Question

How many total numbers of atoms are present in the formula $KAl{(S{0_4})_2}$
A. $7$
B. $9$
C. $11$
D. $12$
E. $13$

Answer 1

Hint: Atoms are so small that they are not visible by naked eyes. Fire, air, water and earth also have their individual atoms which are connected to each other. Law of conservation of mass and law of constant proportion defines the difference between the atoms and molecules.

Complete step by step answer:
All matter could be broken down into four basic substances-fire, air, water and earth. There is something which is smaller than matter. It is common in every substance. Thus the discovery of atoms was introduced. After atoms, certain bigger entities called molecules were discovered.
The law of conservation of mass defines that the mass of a closed system remains constant in a chemical reaction. Molecules are composed of two or more elements or atoms. The proportions in which the atoms are present in a compound remains the same irrespective of its method of preparation.
Atoms of different elements have different physical and chemical properties. Atoms of different elements combine in a small whole number ratio to form compounds. In a given compound, the relative number and types of atoms are constant.
All matter is made up of atoms. Hydrogen is the smallest of all the atoms.
In the given molecule $KAl{(S{0_4})_2}$ it contains potassium, aluminium, sulfur and oxygen atoms.
The number of potassium atoms in the given molecule is $1$.
The number of aluminium atoms in the given molecule is $1$.
The number of sulfur atoms in the given molecule is $2$.
Oxygen atoms $ - 8$
Thus a total of $1 + 1 + 2 + 8 = 12$ atoms are present in the given molecule.

So, the correct answer is Option D .

Note:
Atoms of a given element are identical in size, mass and other properties. In chemical reactions, atoms are combined, rearranged and separated.
This may be confusing with Avogadro number. This is different from the number of atoms in a molecule. One mole of a substance contains Avogadro's number of atoms.