UPSC CSE Prelims
Basic Chemical Concepts Previous Year Questions (PYQs)

Detailed Explanation:

Answer: Option 1 — it is dipolar in nature

Water is known as the "universal solvent" because of its dipolar (polar) nature. Water molecules have a bent structure with partial positive charges on hydrogen atoms and a partial negative charge on the oxygen atom, creating a dipole. This polarity enables water molecules to surround and interact with ions and other polar molecules through electrostatic attraction, effectively separating and dissolving them. The dipolar nature is the fundamental reason why water can dissolve more substances than any other liquid.

📝 Short Notes: Properties of Water as a Solvent

• Dipolar/Polar Nature: Water has a bent molecular structure (H-O-H angle ~104.5°) with oxygen being more electronegative, creating partial charges (δ+ on H, δ- on O).
• Universal Solvent: Water dissolves ionic compounds (like salts) by surrounding ions with water molecules (hydration) and polar covalent compounds through hydrogen bonding.
• Hydrogen Bonding: The polar nature allows water molecules to form hydrogen bonds with each other and with solute particles, facilitating dissolution.
• High Dielectric Constant: Water has a high dielectric constant (~80), which reduces the electrostatic attraction between dissolved ions, keeping them separated in solution.
• Not Related to Solvent Properties: Good heat conductor, high specific heat, and being an oxide of hydrogen are properties of water but not the primary reasons for its exceptional solvent capabilities.

Detailed Explanation:

✅ Statement 1 – Incorrect: Crystallization of sodium chloride is a physical change; NaCl changes from dissolved to solid state without altering its chemical composition.
✅ Statement 2 – Incorrect: Melting of ice is a physical change; H₂O molecules transition from solid to liquid state while maintaining the same chemical structure.
✅ Statement 3 – Correct: Souring of milk is a chemical change; bacteria convert lactose into lactic acid, creating new substances and irreversibly altering the chemical composition.