45. Of the following, which is the smallest particle in an atom?
Answer: B
Electrons are the smallest particles in an atom.
Electrons are subatomic particles with a very small mass, significantly smaller than that of protons and neutrons, making them the smallest particles in an atom.
A) Proton
Protons are positively charged particles found within the nucleus of an atom. They have a relatively large mass compared to electrons and are not the smallest particles in an atom.
B) Electron
Electrons are negatively charged particles that orbit the nucleus of an atom. Their mass is about 1/1836 that of a proton or neutron, which confirms that they are indeed the smallest particles in an atom.
C) Neutron
Neutrons are neutral particles located in the nucleus of an atom. They have a mass similar to that of protons, making them larger than electrons and not the smallest particle.
D) Nucleus
The nucleus is the central part of an atom, composed of protons and neutrons. It is significantly larger than electrons and contains the majority of the atom's mass, thus it is not a particle by itself.
Conclusion
Electrons are definitively the smallest particles in an atom due to their negligible mass compared to protons and neutrons. All other options, including protons, neutrons, and the nucleus itself, are larger in mass and do not qualify as the smallest particles.