Question

The number of neutrons in an atom having mass number 39 and atomic number 19 is ___________.

Answer 1

Atomic number: The total number of protons in the nucleus of an atom gives us the atomic number of that atom. It is represented by '$\mathrm{Z}$'.

Atomic number = Number of protons

The atomic number given in the question is 19, so the number of protons is19.

Mass number: The number of protons and neutrons combine to give us the mass number of an atom. It is represented using the letter ‘$\mathrm{A}$.’

Mass number = number of protons + number of neutrons

Since the mass number given in the question is 39, it is the sum of both protons and neutrons.

Formula to calculate the number of neutrons = mass number (A) - atomic number (Z)

So, the number of neutrons= $39-19$

Number of neutrons= $20$

Therefore, the number of neutrons in an atom having mass number 39 and atomic number 19 is 20.