Question

Almost the entire mass of an atom is concentrated in the:
A.Protons
B.Electrons
C.Neutrons
D.Nucleons

Answer 1

An atom comprises a nucleus and the revolving electrons around it. The nucleus of an atom has protons and neutrons, where the number of protons is equal to the atomic number of an element or atom.

Complete step by step answer:
The primary structure of an atom has protons, neutrons and electrons. Protons and neutrons together make up the nucleus of an electron and are known as nucleons, while electrons remain outside the nucleus of an atom. In a neutral atom, there are equal numbers of protons and electrons present.
Many theories were proposed to describe the atomic structure. After Dalton’s and Thomson’s theory came Rutherford's atomic structure which stated that most of the mass and storage of an atom is concentrated in the nucleus as the shape of an atom is spherical. Electrons just revolve around the nucleus in circular orbit.
He called these three particles as Subatomic particles. Proton is positively charged having mass of $1.672 \times {10^{ - 24}}$ and neutrons are neutral i.e. no charge but have mass of $1.674 \times {10^{ - 24}}$ . Electrons are 1800 times lighter than protons, having mass of $9.1 \times {10^{ - 31}}$ . Therefore, they are neglected at the time of calculating the mass of an atom as electrons have negligible mass.
We can now say that almost the entire mass of an atom is concentrated in the nucleons i.e., protons and neutrons.

Hence, the correct option is (D).

Note:
There exist some more particles in nucleus other than these three because protons and neutrons are made up of particles called quarks. These are found in baryons, mesons and plasmas. A proton has two up quarks and one down quark.