Question

Relative atomic mass of calcium is approximately __________ its atomic number.
(a) Equal
(b) Twice
(c) Thrice
(d) None of these

Answer 1

Hint: 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.

Complete answer:
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, the calcium is the element of group 2 of the s-block and its atomic number is 20. This means that the number of protons in the calcium atom is 20. So, the number of electrons will also be 20. We know that the number of neutrons in the calcium is 20, hence we can calculate the relative atomic mass.
$\text{Atomic mass = No}\text{. of protons + No}\text{. of neutrons}$
$\text{Atomic mass = 20 + 20}$
$\text{Atomic mass = 40}$
So, the atomic mass is 40, which is double or twice the atomic number.

Therefore, the correct answer is an option (b)- Twice.

Note:
The number of neutrons doesn't need to be always equal to the number of protons in the atom. When the number of neutrons in the same atom changes, it leads to the formation of isotopes like in hydrogen atoms.