Question

Arrange the following acids in decreasing order of their $ p{{K}_{a}} $ values

• A. IV, III, II, I
• B. II, I, IV, III
• C. II, I, III, IV
• D. I, II, IV, III

Answer 1

Answer: (C)

The acidity increases on decreasing the value of $ p{{K}_{a}} $ . $ \underset{acetic\text{ }acid}{\mathop{C{{H}_{3}}COOH}}\,<\underset{formic\text{ }acid}{\mathop{HCOOH}}\,<\underset{chloroacetic\text{ }acid}{\mathop{ClC{{H}_{2}}COOH}}\, $ $ <\underset{\begin{smallmatrix} trichloroacetic \\ \,\,\,\,\,\,\,\,\,\,\,acid \end{smallmatrix}}{\mathop{C{{l}_{3}}C.COOH}}\, $ $ \xrightarrow[Increasing\text{ }order\text{ }of\text{ }acidic\text{ }strength]{{}} $ or Decreasing order of $ p{{K}_{a}} $ .