Question

Arrange the following compounds in order of their increasing acid strength

• A. I $<$ II $<$ III $<$ IV
• B. IV $<$ III $<$ II $<$ I
• C. I $<$ IV $<$ II $<$ III
• D. II $<$ I $<$ III $<$ IV

Hint:

Using a simple frame or just bolding for the box
Key Points:
Acid strength increases with the stability of the conjugate base.
The -COOH group has an electron-withdrawing inductive effect (-I).
In dicarboxylic acids, the -I effect of one -COOH group stabilizes the conjugate base formed by the ionization of the other -COOH group.
The inductive effect decreases significantly with increasing distance (number of separating CH$_2$ groups).
Acidity Order: Oxalic>Malonic>Succinic>Adipic.