An element ‘X’ belongs to 3rd period and group 16 of the Modern Periodic Table. (a) Determine the number of valence electrons and the valency of ‘X’. (b) Molecular formula of the compound when ‘X’ reacts with hydrogen and write its electron dot structure. (c) Name the element ‘X’ and state whether it is metallic or non-metallic.

(a) Valence electrons and Valency of 'X':

• Since element 'X' belongs to Group 16 and Period 3, its atomic number is $16$.
• Its electronic configuration is $2, 8, 6$.
• Number of valence electrons = $6$
• Valency = $8 - 6 = 2$

(b) Molecular Formula and Electron Dot Structure:

• When 'X' (Sulphur, $S$) reacts with hydrogen ($H$, valency $1$), it forms hydrogen sulphide.
• Molecular formula: $H_2S$
• Electron dot structure:

Sulphur has $6$ valence electrons and requires $2$ more to complete its octet. Each hydrogen atom has $1$ valence electron and requires $1$ more to complete its duplet. They share electrons to form two single covalent bonds:

$$\text{H} : \ddot{\text{S}} : \text{H}$$

(where the dots represent the valence electrons of Sulphur and Hydrogen participating in covalent sharing, leaving two lone pairs on the Sulphur atom).

(c) Name and Classification of 'X':

• Name of the element: Sulphur ($S$)
• Classification: Non-metallic. It is a non-metal because it has $6$ valence electrons and readily gains or shares electrons to complete its octet.