Question

Which atom contains exactly 15 neutrons?
A. $ {P^{32}}{\text{(atomic number}} = 17{\text{)}} $
B. $ {S^{32}}{\text{(atomic number}} = 16{\text{)}} $
C. $ {O^{15}}{\text{(atomic number}} = 8{\text{)}} $
D. $ {N^{15}}{\text{(atomic number}} = 7{\text{)}} $

Answer 1

Hint: In order to find out which atom contains exactly 15 neutrons we must know how to calculate the number of neutrons, protons and as well as electrons present in the nucleus of an atom, we must should have the concepts such as the atomic number and the mass number of the atom. From this we can easily calculate the neutrons, electrons and protons present and hence our required answer too.

Complete answer:
As we know, the mass number is nothing but the sum of the number of protons and the number of neutrons.
So, let us check one by one,
Option A:
Given that mass number of $ P = 32 $
And we know that, atomic number (no. of electrons is equal to the no. of protons) which is in this case is $ 17 $
Therefore no. of neutrons $ = 32 - 17 = 15 $
As we can see, this option is correct.
Option B:
Given that mass number of $ S = 32 $
And we know that, atomic number (no. of electrons is equal to the no. of protons) which is in this case is $ 16 $
Therefore no. of neutrons $ = 32 - 16 = 16 $
As we can see, this option is not correct.
Option C:
Given that mass number of $ O = 15 $
And we know that, atomic number (no. of electrons is equal to the no. of protons) which is in this case is $ 8 $
Therefore no. of neutrons $ = 15 - 8 = 7 $
As we can see, this option is not correct.
Option D:
Given that mass number of $ N = 15 $
And we know that, atomic number (no. of electrons is equal to the no. of protons) which is in this case is $ 7 $
Therefore no. of neutrons $ = 15 - 7 = 8 $
As we can see, this option is not correct.
Hence, from the above solution we can say that option A is the correct option.

Note:
The mass of an atom of any element is concentrated in its nucleus, as we all know. As a result, an atom's mass number is determined by the nucleus' composition. It indicates that an atom's mass number is determined by the number of protons and neutrons in its nucleus. Nucleons are made up of protons and neutrons. As a result, the mass number can be defined as the total number of protons and neutrons in an atom's nucleus.
Mass number = Number of protons + Number of neutrons
Which is also called Number of nucleons.