Question

Number of protons, neutrons and electrons in the element ${}_{89}^{231}Y$ is,
A) 89, 231, 89
B) 89, 89, 242
C) 89, 142, 89
D) 89, 71, 89

Answer 1

In the given element, the atomic number is 89 and this number is related to number of protons.
- The mass number of the element is 231 from which we can get the value of neutrons.

Complete Solution :
So here in the question we are given an element having the atomic number 89 and mass number 231 and we have to predict the number of protons, neutrons and electrons present on each atom of the element.
- To brush our memory let's discuss some basic concepts about the mass number, atomic number, its calculations and about the charge related to electrons, protons and neutrons.
- We know that the atoms contain many subatomic particles but the important three subunits which are of our concern are electrons, protons and neutrons.
- Electrons are negatively charged particles which are present in the orbitals of the atom and are represented as ${{e}^{-}}$. Its magnitude is said to have the value -1.
- Protons are positively charged subatomic particles present in the atom. The protons are present in the nucleus of the atom around which the counter ions i.e. electrons are revolving. Protons are generally represented as ${{p}^{+}}$, having a magnitude of +1.
- Neutrons are neutral species which are present in the nucleus of an atom. So the nucleus of an atom comprises both neutrons and protons and the nucleus is a positively charged massive unit of an atom.
Now let’s discuss the relation between the atomic mass number and atomic number with the number of electrons, protons and neutrons.
- Atomic number in an element is the unique value by which we can identify an element, the value of atomic number is unique for each element and it’s the identity of an element and it is usually represented as Z.
Atomic number of an element is equal to the number of electrons or number of protons in an atom.
Z = number of electrons = number of protons.
- An element possesses an equal number of electrons and protons.
By the data discussed above we know that the nucleus consists of both neutrons and protons and hence the atomic mass is equal to the number of neutrons and protons present in an atom.
$\text{Atomic mass = number of protons + number of neutrons}$
- Now let’s solve the question, we know the atomic number of the element is 89 and the mass number is 231.
Since the atomic number is 89.
Z=89= number of electrons = number of protons.
Number of protons = 89
Number of electrons = 89
Now the atomic mass is 231 amu which is equal to the number of protons and neutrons.
$\text{Atomic mass = number of protons+number of neutrons}$
$\text{231 = 89 + number of neutrons}$
$\text{Number}\,\text{of}\,\text{neutrons=231-89=142}$
So, the correct answer is “Option C”.

Note: While doing problems related to atomic mass, atomic number, number of electrons, neutrons and protons etc. we are concerned only about the magnitude, we do not take into consideration the charge of the sub-atomic species.