For the dissociation of a weak acid HA, the degree of dissociation α is given (approximately, when α ≪ 1) by:
Aα = √(K_a / C)
Bα = K_a / C
Cα = √(K_a · C)
Dα = C / K_a
Answer & Solution
Correct answer: A. α = √(K_a / C)
1. HA ⇌ H⁺ + A⁻; K_a ≈ C α² / (1 − α).
2. For α ≪ 1, (1 − α) ≈ 1 and K_a ≈ C α² ⇒ α = √(K_a / C).
3. Hence dilute solutions (small C) have larger α — Ostwald's dilution law.
_Source: NCERT Class 11 Chem Ch 7 §7.10 Ostwald's Dilution Law_
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