Match the atomic numbers 4, 8, 10, 15 and 19 with each of the following:

(a) Element which can form trivalent ion.

(b) An element with 4 shells.

(c) Element with 6 valence electrons.

(d) Element which does not form an ion.

Identify the following reactions as either oxidation or reduction:

(i) O + 2e^- ⟶ O^2-

(ii) K - e^- ⟶ K⁺

(iii) Fe³⁺ + e^- ⟶ Fe²⁺

(iv) Zn ⟶ Zn²⁺ + 2e^-

Name or state the following.

(a) An element having valency zero.

(b) Metal with valency one.

(c) Atoms of the same element differing in mass numbers.

(d) Elements having same mass number but different atomic number.

(e) Bond formed by transfer of electrons(s)

(f) Ion formed by gain of electron(s)

(a) Define covalent (molecular) bond.

(b) Give an example of covalent bond formed by

(i) similar atoms

(b) dissimilar atoms