The correct order of boiling point is:

Options

A. `T_(2)ltD_(2)gtH_(2)`
B. n-pentane`lt`neo-pentane
C. `XeltArltHe`
D. m-nitrophenol`gt` o-nitrophenol

Explanation

To determine the correct order of boiling points among the given substances, we can analyze the factors affecting boiling points, such as molecular weight, branching in molecular structure, and types of intermolecular forces present. Here’s a step-by-step solution:

### Step 1: Analyze the first set of compounds (Protium, Deuterium, and Tritium)
- **Protium (H)** has a molecular weight of 1.
- **Deuterium (D)** has a molecular weight of 2.
- **Tritium (T)** has a molecular weight of 3.

**Boiling Point Order**: The boiling point increases with increasing molecular weight. Therefore, the order is:
- Tritium > Deuterium > Protium

### Step 2: Analyze the second set of compounds (n-Pentane and Neopentane)
- **n-Pentane** is a straight-chain alkane (C5H12) with no branching.
- **Neopentane** is a branched alkane (C5H12) with a more compact structure.

**Boiling Point Order**: Straight-chain alkanes have higher boiling points than their branched counterparts due to greater surface area and stronger London dispersion forces. Therefore, the order is:
- n-Pentane > Neopentane

### Step 3: Analyze the third set of compounds (Xenon, Argon, and Helium)
- **Helium (He)** has a molecular weight of 4.
- **Argon (Ar)** has a molecular weight of 40.
- **Xenon (Xe)** has a molecular weight of 131.

**Boiling Point Order**: The boiling point increases with increasing molecular weight. Therefore, the order is:
- Xenon > Argon > Helium

### Step 4: Analyze the fourth set of compounds (Meta-nitrophenol and Ortho-nitrophenol)
- **Ortho-nitrophenol** has intramolecular hydrogen bonding due to the proximity of the -OH and -NO2 groups.
- **Meta-nitrophenol** does not have this intramolecular hydrogen bonding and relies on intermolecular hydrogen bonding.

**Boiling Point Order**: The presence of intramolecular hydrogen bonding in ortho-nitrophenol makes it less stable than meta-nitrophenol, which can form stronger intermolecular hydrogen bonds. Therefore, the order is:
- Meta-nitrophenol > Ortho-nitrophenol

### Final Conclusion
Based on the analysis above, the correct order of boiling points for the given compounds is:
1. Tritium > Deuterium > Protium
2. n-Pentane > Neopentane
3. Xenon > Argon > Helium
4. Meta-nitrophenol > Ortho-nitrophenol