(a) Element A has an atomic number of 6, so its electronic configuration is 2,4 (having 4 valence electrons).
Therefore, the group number for element A = valence shell + 10
= 4+10 =14.
Hence, the group number for element A is 14.
Element B has 17 electrons in its neutral atom. Its electronic configuration is 2,8,7.
Therefore, the group number of element B = valence shell + 10
= 7 + 10 = 17.
Hence, the group number for element B is 17.
(b) When two non-metals A and B combine, a covalent bond is formed, since group 14 elements and group 17 elements are all non-metallic in nature.
(c) When one atom of A combines with four atoms of B, a covalent compound with the formula AB4 is formed. This is because the element A has a valency of 4 and element B has a valency of 1.