(a) (i) Write two properties of gold which make it the most suitable metal for ornaments. (ii) Name two metals which are the best conductors of heat. (iii) Name two metals which melt when you keep them on your palm. (b) Explain the formation of ionic compound CaO with electron-dot structure. Atomic numbers of calcium and oxygen are 20 and 8 respectively.

Part (a)

(i) Two properties of gold which make it the most suitable metal for ornaments:

1. High Malleability and Ductility: Gold is the most malleable and ductile metal known. A wire of about $2\text{ km}$ length can be drawn from just one gram of gold, allowing artisans to design highly intricate and delicate patterns.
2. Chemical Inertness (Corrosion Resistance) and Lustre: Gold has a brilliant, long-lasting metallic lustre and does not react with oxygen, moisture, or acids even at high temperatures. This ensures that ornaments do not tarnish or corrode over time.

(ii) Two metals which are the best conductors of heat:

• Silver ($Ag$) and Copper ($Cu$).

(iii) Two metals which melt when kept on the palm:

• Gallium ($Ga$) and Caesium ($Cs$).

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Part (b) Formation of Ionic Compound $CaO$ (Calcium Oxide)

1. Electronic Configurations:

• Calcium ($Ca$, Atomic Number = $20$):
• Electronic configuration: $2, 8, 8, 2$
• Valence electrons: $2$
• To achieve a stable octet configuration, a calcium atom loses its $2$ valence electrons to form a calcium cation ($Ca^{2+}$):

$$Ca \rightarrow Ca^{2+} + 2e^{-}$$

$$\text{(2, 8, 8, 2)} \rightarrow \text{(2, 8, 8)}$$

• Oxygen ($O$, Atomic Number = $8$):
• Electronic configuration: $2, 6$
• Valence electrons: $6$
• To achieve a stable octet configuration, an oxygen atom gains $2$ electrons to form an oxide anion ($O^{2-}$):

$$O + 2e^{-} \rightarrow O^{2-}$$

$$\text{(2, 6)} \rightarrow \text{(2, 8)}$$

2. Electron-Dot Transfer Diagram:

Calcium transfers its $2$ valence electrons to the oxygen atom, which requires $2$ electrons to complete its octet:

$$\text{Ca}^{\bullet \bullet} + \cdot \cdot \ \ddot{\text{O}} \ \cdot \cdot \longrightarrow \text{Ca}^{2+} \left[ :\ddot{\text{O}}: \right]^{2-} \text{ or } \text{CaO}$$