Which of the following statements are correct ?

Options

A. Oximes are stronger acid than hydroxylamine.
B. `pK_a` of maleic acid is less than `pK_a` of fumaric acid.
C. `Me_3 SiCH_2 COOh` is a stronger acid than `Me_3 C-CH_2 COOH`.
D. o-Nitrobenzoic acid is a weaker acid than 3,5-dinitrobenzoic acid.

Answer

To determine which of the statements regarding acids are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement A: Oximes are stronger acids than hydroxylamine.**
- Hydroxylamine (NH2OH) has no significant electron-withdrawing groups that enhance acidity. In contrast, oximes (R1R2C=NOH) have a double bond between nitrogen and carbon, which can exhibit a -I (inductive) effect due to the electronegativity of the nitrogen atom. This -I effect stabilizes the conjugate base formed after deprotonation, making oximes stronger acids than hydroxylamine.
- **Conclusion:** Statement A is correct.

2. **Statement B: pKa of malic acid is less than pKa of fumaric acid.**
- Malic acid is the cis isomer of butanedioic acid, while fumaric acid is the trans isomer. The conjugate base of malic acid is stabilized by intramolecular hydrogen bonding, making it a stronger acid than fumaric acid, whose conjugate base lacks such stabilization. Therefore, a lower pKa value indicates that malic acid is indeed a stronger acid than fumaric acid.
- **Conclusion:** Statement B is correct.

3. **Statement C: Silicon forms stronger acids than carbon.**
- Silicon (Si) is less electronegative than carbon (C). The lower electronegativity of silicon means that it does not stabilize the negative charge on the conjugate base as effectively as carbon does. Consequently, silicon-based acids are generally weaker than their carbon counterparts.
- **Conclusion:** Statement C is incorrect.

4. **Statement D: Ortho-nitrobenzoic acid is weaker than 3,5-dinitrobenzoic acid.**
- The nitro group (NO2) is a strong -M (mesomeric) and -I (inductive) electron-withdrawing group, which increases the acidity of benzoic acids. In 3,5-dinitrobenzoic acid, there are two nitro groups that enhance the acidity more than the single nitro group in ortho-nitrobenzoic acid. Hence, 3,5-dinitrobenzoic acid is indeed a stronger acid than ortho-nitrobenzoic acid.
- **Conclusion:** Statement D is correct.

### Final Answer:
The correct statements are A, B, and D.

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