Concept: This question compares the physical properties of electrovalent (ionic) compounds with covalent compounds, specifically focusing on melting and boiling points.

Why (A) is correct: Electrovalent compounds are formed by the complete transfer of electrons, leading to the formation of positively and negatively charged ions. These ions are held together by strong electrostatic forces of attraction in a crystal lattice structure. A large amount of energy is required to overcome these strong forces and break down the crystal lattice, which is necessary for melting (transition from solid to liquid) and boiling (transition from liquid to gas). Therefore, electrovalent compounds generally have high melting points (m.p.) and high boiling points (b.p.) compared to covalent compounds, which are held together by weaker intermolecular forces.

Option Analysis:

• A) High m.p. and high b.p.: This is correct. Strong electrostatic forces in ionic compounds require significant energy to overcome.
• B) Low m.p. and low b.p.: This describes typical covalent compounds, which have weaker intermolecular forces.
• C) Low m.p. and high b.p.: This combination is generally not characteristic of either pure ionic or pure covalent compounds.
• D) High m.p. and low b.p.: This combination is also generally not characteristic of either pure ionic or pure covalent compounds.

Correct Answer: (A)