GENERAL KNOWLEDGE

Detailed explanation-1: -The element with the smallest atomic mass is hydrogen (H), which is made up of protons and electrons, two types of subatomic particles.

Detailed explanation-2: -The lightest chemical element is Hydrogen and the heaviest is Hassium.

Detailed explanation-3: -Therefore helium has the smallest atomic size.

Detailed explanation-4: -d) Electron: It is the sub atomic particle of an atom but it cannot retain its chemical properties. From the above information we can conclude that atom is the smallest unit of matter and hence option B is correct.