Differentiate between the following terms.

Atomic number and mass number

Name or state the following.

1. The three isotopes of hydrogen.
2. Two elements having same number of protons and electrons but different number of neutrons.
3. The valency of an element whose electronic configuration is 2, 8, 3.
4. The shell closest to the nucleus of an atom.
5. An element having valency zero.

Differentiate between the following terms.

Nucleus and nucleons

Differentiate between the following terms.

Octet and duplet