The correct electronic configuration of Fluorine is:

1. 2, 8
2. 8, 2, 1
3. 7, 2
4. 2, 7

An element 'A' has 15 electrons and 16 neutrons. The correct representation of this element is:

1. ¹⁶₁₅A
2. ³¹₁₆A
3. ³¹₁₅A
4. ¹⁵₁₆A

Elements with valency 2 are:

1. Always metals
2. Always non-metals
3. Can be metals or non-metals
4. Metalloids (semi metals)

Nucleus of an atom is composed of :

1. Electrons and neutrons
2. Protons and neutrons
3. Protons, neutrons and electrons
4. Electrons and protons