Question

How many neutrons does calcium have?

Answer 1

Hint: For an atom Atomic number (${\text{Z}}$) is always equal to the number of electrons or number of protons and Atomic mass (${\text{A}}$) is equal to the sum of the number of neutrons and protons.

Complete answer:
In the periodic table calcium is denoted as
${}_{{\text{20}}}^{{\text{40}}}{\text{Ca}}$, where upper quantity describes the atomic mass (${\text{A}}$) and lower quantity describes the atomic number (${\text{Z}}$).
-As we know that:
 Atomic number (${\text{Z}}$) = No. of electrons = No. of protons
From above relation it is clear that, number of electrons which are present outside the nucleus in the orbital of calcium atom is equal to $20$ and number of protons which are present inside the nucleus is also equal to $20$, because the atomic number (${\text{Z}}$) of silver is $20$.
-Relation between atomic mass, protons and neutrons are described as follow:
Atomic mass (${\text{A}}$) = No. of protons + No. of neutrons
It is known that, atomic mass of calcium = $40$
And also we know that number of protons in calcium = $20$
So, number of neutrons = Atomic mass (${\text{A}}$) - No. of protons
No. of neutrons = $40 - 20 = 20$.
Hence $20$ neutrons are present in calcium.

Note:
 Here some of you may get confuse in the values of atomic mass (${\text{A}}$) and atomic number (${\text{Z}}$) which is denoted in the symbol of calcium, so always keep in mind higher value always describes the atomic mass.