In case of chlorine ${}^{35}C{l_{17}}$ with atomic number $Z = 17$ and mass number $A = 35$ has number of neutron equal to___________
A) \[\left( {\text{A}} \right)17\]
B) \[\left( {\text{B}} \right){\text{ }}35\]
C) \[\left( {\text{C}} \right){\text{ }}18\]
D) \[\left( {\text{D}} \right){\text{ }}20\]

Hint:According to Rutherford, the central core of the atom which contains the entire positive charge, and most of its mass is known as the atomic nucleus. The size of the nucleus is much smaller than that of an atom. Thus, a nucleus occupies a very small space in the atom.

Complete step by step answer:
As we all know, the nucleus is composed of protons and neutrons. A proton is a positively charged particle and has a charge equal to that of an electron. The mass of a proton is about \[1836\] times that of an electron.
The atomic number of an element is the number of protons present inside the nucleus of an atom of the element. In the case of a neutral atom, the atomic number is also equal to the number of electrons revolving around the nucleus of the atom.
\[z\] is represented by the atomic number of an element. The mass number of an element is the total number of protons and neutrons present inside the nucleus of an atom of the element. \[a\] is represented by the mass number of an element. Therefore, the number of neutrons in the atom is $N = A - Z....\left( 1 \right)$
A nucleus is represented by${}_Z{X^A}$ where\[\;x\] is the chemical symbol of the element.
Given, a chlorine${}^{35}C{l_{17}}$ with atomic number $Z = 17$ and mass number $A = 35$
Substitute these values in the equation$\left( 1 \right)$, we can calculate,
The number of neutrons, $N = A - Z$
$ \rightarrow N = 35 - 17$
On subtracting we get,
$ \rightarrow N = 18$
Hence, the number of neutrons in the atom is $18$

The correct option is C

Additional information:
-Isotopes: The isotopes of an element are the atoms of the element which have the same atomic number but a different mass number. Hence, the isotopes of the atomic weights of an element are different. Isotopes of the same element have the same chemical properties but may not have the same nuclear and physical properties.
-Isobars: The same mass number but different atomic numbers that have the atoms of different elements which are called isobars. The chemical properties of isobars are widely different because they have different numbers and arrangements of electrons. Their physical properties may be identical.
-Isotones: Isotones having the same number of neutrons that are the nuclei.

Note:
-The total mass of nucleons present in a nucleus is called nuclear mass.
-Protons and neutrons in a nucleus are called nucleons.
-Neutron is discovered by Chadwick in \[1932\] .