An atom of an element has 9 protons, 9 electrons and 10 neutrons. State its

(a) atomic number

(b) mass number and

(c) electronic configuration.

Sulphur has an atomic number 16 and mass number of 32. State the number of protons and neutrons in the nucleus of sulphur. Give a simple diagram to show the arrangement of electrons in an atom of sulphur.

Rutherford's alpha-particle scattering experiment led to the discovery of :

1. Electron
2. Proton
3. Atomic nucleus
4. Neutron

The number of valence electrons in O^2- is :

1. 6
2. 8
3. 10
4. 4