Question

Calculate the ratio of atomic masses of Sulphur and Oxygen.
A) 1
B) 2
C) 3
D) 4

Answer 1

Hint: Atomic mass is the mass of any element expressed in atomic mass unit (amu).
It is also nearly equal to addition of protons and neutrons in an element.
In the case of isotopes, atomic mass will become the average atomic mass of the isotopes according to their composition in nature.

Complete answer:
First we have to find out the atomic mass of sulphur and oxygen. After this we can take a ratio of the stomach masses of sulphur and oxygen.
For Sulphur (S), Atomic number = 16,
So, Number of electrons = Number of protons = 16,
And, Number of neutrons = 16
Thus, Atomic mass of Sulphur = 16 + 16 = 32 amu
For Oxygen (O), Atomic number = 8,
So, Number of electrons = Number of protons = 8,
And, Number of neutrons = 8
Thus, Atomic mass of Oxygen = 8 + 8 = 16 amu
Now, Ratio =${\dfrac{ Atomic\; mass\; of\; sulphur}{ Atomic\; mass\; of \;Oxygen}}$
=${\dfrac{ 32}{16}}$ = 2

Thus, the correct option is (B).

Note: We know that the size of an atom is extremely small, so it is difficult to measure the atomic mass in a unit of Kilogram or gram. So there is unit called amu or atomic mass unit.
Also, to find masses of elements, we needed some reference point, so we have taken isotope of carbon, C-12 and its atomic mass is taken as 12 units.
Other atomic masses are measured in reference to C-12.