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 compounds, we need to analyze the factors affecting boiling points, such as molecular weight and molecular structure, particularly branching and hydrogen bonding.

### Step-by-Step Solution:

1. **Understanding Boiling Point Factors**:
- Boiling point is influenced by molecular weight and the structure of the molecules.
- Generally, a higher molecular weight corresponds to a higher boiling point.
- Increased branching in a molecule typically results in a lower boiling point due to decreased surface area and weaker van der Waals forces.

2. **Analyzing the First Set of Compounds (Tritium, Deuterium, Hydrogen)**:
- Tritium (T) has an atomic weight of 3.
- Deuterium (D) has an atomic weight of 2.
- Hydrogen (H) has an atomic weight of 1.
- Since boiling point is directly proportional to molecular weight, the order of boiling points should be T > D > H.

3. **Analyzing the Second Set of Compounds (n-pentane vs. neopentane)**:
- n-pentane is a straight-chain alkane with five carbon atoms.
- Neopentane is a branched alkane with the same number of carbon atoms but a more compact structure.
- The straight-chain structure of n-pentane allows for stronger van der Waals forces compared to the branched neopentane, leading to a higher boiling point for n-pentane.

4. **Analyzing the Third Set of Compounds (meta-nitrophenol vs. ortho-nitrophenol)**:
- Meta-nitrophenol can form intermolecular hydrogen bonds, which are stronger and increase boiling point.
- Ortho-nitrophenol can form intramolecular hydrogen bonds, which are generally weaker than intermolecular hydrogen bonds.
- Therefore, meta-nitrophenol has a higher boiling point than ortho-nitrophenol due to the presence of stronger intermolecular hydrogen bonding.

5. **Conclusion**:
- Based on the analysis, the correct order of boiling points from highest to lowest is:
- Meta-nitrophenol > Ortho-nitrophenol > n-pentane > Neopentane > Tritium > Deuterium > Hydrogen.

### Final Order of Boiling Points:
1. Meta-nitrophenol
2. Ortho-nitrophenol
3. n-Pentane
4. Neopentane
5. Tritium (T)
6. Deuterium (D)
7. Hydrogen (H)