Question

The ratio of mass of sulfur and oxygen in $S{{O}_{2}}$ is:
(a)- 1 : 2
(b)- 2 : 1
(c)- 1 : 1
(d)- 1 : 4

Answer 1

Hint: The atomic number of sulfur is 16 and its atomic mass is 32, and in $S{{O}_{2}}$ only one sulfur atom is present. The atomic number of oxygen is 8 and its atomic mass is 16, and in $S{{O}_{2}}$ there are two oxygen atoms.

Complete Solution :
A chemical element is represented by two things: atomic number and atomic mass. The atomic mass is always written as the superscript to the symbol of the element and the atomic number is always written as the subscript to the symbol of the element.
- The atomic number of the element is always equal to the number of protons present in the atom or the number of electrons present in the atom, but the atomic mass or relative atomic mass can be calculated by adding the number of neutrons to the number of protons.
- So, both sulfur and oxygen belong to the same group 16 of the p-block, and their atomic numbers are 16 and 8 respectively. There are 16 neutrons in sulfur and 8 neutrons in oxygen, therefore, the atomic mass of sulfur and oxygen will be 32 and 16 respectively.
- In $S{{O}_{2}}$, one sulfur atom is present, so the mass of sulfur will be 32 and there are 2 oxygen atoms, so the mass of oxygen will be: 16 + 16 = 32.
Now, taking the ratio:
$32:32\text{ }=\text{ 1: 1}$
So, the correct answer is “Option C”.

Note: Don't forget to multiply the number of atoms of the specific element in the compound to get its total mass in the compound. If the ratio of the atomic number is given, then multiplication is not required.