Which type of material is a good conductor of heat and electricity in solid and liquid states, is insoluble in water, and typically has a high melting point?
Correct Answer: \( \boxed{\mathrm{D}} \)
Metallic materials contain a lattice of positive metal ions surrounded by delocalised electrons.
The delocalised electrons are able to move through the structure, allowing metals to conduct both heat and electricity.
Metallic substances are generally insoluble in water and often have high melting points because of the strong electrostatic attraction between the positive metal ions and delocalised electrons.
Therefore, the correct answer is (D).
Which statement best explains the malleability of magnesium metal?
Correct Answer: \( \boxed{\mathrm{C}} \)
Magnesium has a giant metallic lattice consisting of positive magnesium ions surrounded by a sea of delocalised electrons.
When a force is applied to the metal, the layers of magnesium ions can move or slide past one another while the metallic bonding is maintained by the delocalised electrons.
This ability of the layers to slide without the lattice completely breaking apart explains the malleability of magnesium.
Therefore, the correct answer is (C).
Metallic bond strength increases with higher charge density (smaller atomic radius and greater charge).
Al³⁺ (Al) > Mg²⁺ (Mg) > Na⁺ (Na) > K⁺ (K)
✅ Answer: (A)
