Question

Which among the following is a pair of dicarboxylic acids?

• A. Glutaric acid and Malonic acid
• B. Succinic acid and Valeric acid
• C. Oxalic acid and Caproic acid
• D. Propionic acid and Adipic acid

Hint:

Use the classic mnemonic phrase "Oh My Stars, Go Ahead" to recall the homologous series of straight-chain dicarboxylic acids in increasing order of carbon count: Oxalic (2C), Malonic (3C), Succinic (4C), Glutaric (5C), and Adipic (6C).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks us to identify the pair in which both organic compounds are classified as dicarboxylic acids (compounds containing exactly two carboxylic acid, $-\mathrm{COOH}$, functional groups).

Step 2: Key Formula or Approach:
Aliphatic dicarboxylic acids have the general molecular formula $\mathrm{HOOC-(CH_2)}_n\mathrm{-COOH}$. Monocarboxylic acids have only one $-\mathrm{COOH}$ group. Let's remember the common names of straight-chain dicarboxylic acids using a sequential carbon count shortcut.

Step 3: Detailed Explanation:
Let's analyze the structures of the acids listed across all choices:
Malonic acid: A 3-carbon dicarboxylic acid, $\mathrm{HOOC-CH_2-COOH}$.
Glutaric acid: A 5-carbon dicarboxylic acid, $\mathrm{HOOC-(CH_2)_3-COOH}$. Both components in option (A) are dicarboxylic acids.
Succinic acid (4 carbons) and Adipic acid (6 carbons) are also dicarboxylic acids.
However, Valeric acid (5 carbons), Caproic acid (6 carbons), and Propionic acid (3 carbons) are regular aliphatic monocarboxylic acids with only a single terminal $-\mathrm{COOH}$ group. Thus, options (B), (C), and (D) each contain one monocarboxylic acid, making them incorrect.

Step 4: Final Answer:
The pair consisting exclusively of dicarboxylic acids is Glutaric acid and Malonic acid, which perfectly matches option (A).