What will be the decreasing order of basic strength of the following conjugate bases? ⁻OH,RO̅,CH₃COO̅,Cl

Solution

Chemistry ma’am · 3 steps

Judge each anion by its conjugate acid: the weaker that acid, the stronger the anion as a base.

1. The rule. A strong acid holds its proton loosely, so its anion has little pull for H⁺ and is a weak base. A weak acid holds H⁺ tightly, so its anion is a strong base.

   Base	Conjugate acid	Approx. pKₐ	Why
   RO⁻	ROH	about 16 to 18	alkyl group pushes electrons (+I) onto O, so the charge is less stable
   OH⁻	H₂O	15.7	no alkyl push, so slightly more stable than RO⁻
   CH₃COO⁻	CH₃COOH	4.76	charge spread over two O atoms by resonance
   Cl⁻	HCl	about -7	HCl is a strong acid, so Cl⁻ is a very stable, very weak base

2. Rank the acids. Acid strength increases as ROH < H₂O < CH₃COOH < HCl. Base strength runs the opposite way.
3. So. The decreasing order of basic strength is RO⁻ > OH⁻ > CH₃COO⁻ > Cl⁻, which is option (d).

The idea to keep. To rank bases, rank their conjugate acids and flip the order. A more stable anion (resonance, electronegativity, size) means a weaker base.

Answer from the NTA final answer key. Solution by PrepWiser.