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Values of dissociation constant, K_a are given as follows : array lc Acid & K _ a HCN & 6.2 10⁻¹⁰ HF & 7.2 10⁻⁴ HNO ₂ & 4.0 10⁻⁴ array Correct order of increasing base strength of the base CN ⁻, F ⁻ and NO ₂⁻ will be :

Options

  1. AF ⁻ < CN ⁻ < NO ₂⁻
  2. BNO ₂⁻ < CN ⁻ < F ⁻
  3. CF ⁻ < NO ₂⁻ < CN ⁻
  4. DNO ₂⁻ < F ⁻ < CN ⁻

Correct answer

C. F ⁻ < NO ₂⁻ < CN ⁻

Step-by-step solution

Higher the value of K _a lower will be the value of pK _ a i.e. higher will be the acidic nature. Further since CN ⁻, F ⁻ and NO ₂⁻ are conjugate base of the acids HCN , HF and HNO ₂ respectively hence the correct order of base strength will be F ⁻ < NO ₂⁻ < CN ⁻ ( stronger the acid weaker will be its conjugate base)

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