The correct order of boiling point is

Options

A. `T_(2) lt D_(2) lt H_(2)`
B. `"n - pentane" lt "neo - pentane"`
C. `Xe lt Ar lt He`
D. `"m - nitrophenol "gt " o - nitrophenol"`

Answer

To determine the correct order of boiling points among the given substances, we will analyze the boiling points of the isotopes of hydrogen, n-pentane and neopentane, noble gases (helium, argon, xenon), and metanitrophenol and orthonitrophenol step by step.

### Step 1: Analyzing Isotopes of Hydrogen
1. **Identify the Isotopes**: The isotopes of hydrogen are Tritium (T), Deuterium (D), and Hydrogen (H).
2. **Determine Their Masses**:
- Tritium (T) has a mass of 3.
- Deuterium (D) has a mass of 2.
- Hydrogen (H) has a mass of 1.
3. **Boiling Point Order**: Since boiling point increases with mass, the order of boiling points is:
- Tritium > Deuterium > Hydrogen

### Step 2: Analyzing n-Pentane and Neopentane
1. **Identify Structures**:
- n-Pentane: CH3-CH2-CH2-CH2-CH3 (linear structure).
- Neopentane: (CH3)4C (highly branched structure).
2. **Effect of Branching**:
- n-Pentane has a larger surface area compared to neopentane due to its linear structure.
- Neopentane has more branching, which decreases surface area and thus decreases Van der Waals forces.
3. **Boiling Point Order**: Therefore, the boiling point order is:
- n-Pentane > Neopentane

### Step 3: Analyzing Noble Gases
1. **Identify the Noble Gases**: Helium (He), Argon (Ar), and Xenon (Xe).
2. **Mass Comparison**:
- Helium < Argon < Xenon (increasing mass).
3. **Boiling Point Order**: As mass increases, boiling point also increases:
- Helium < Argon < Xenon

### Step 4: Analyzing Metanitrophenol and Orthonitrophenol
1. **Identify Structures**:
- Ortho-nitrophenol: Nitro group is on the ortho position relative to the hydroxyl group.
- Meta-nitrophenol: Nitro group is on the meta position relative to the hydroxyl group.
2. **Hydrogen Bonding**:
- Ortho-nitrophenol has intramolecular hydrogen bonding (within the molecule).
- Meta-nitrophenol has intermolecular hydrogen bonding (between different molecules).
3. **Boiling Point Order**: The presence of intramolecular hydrogen bonding in ortho-nitrophenol leads to lower boiling points compared to the intermolecular hydrogen bonding in meta-nitrophenol:
- Meta-nitrophenol > Ortho-nitrophenol

### Final Summary of Boiling Point Orders
- For isotopes of hydrogen: Tritium > Deuterium > Hydrogen
- For n-pentane and neopentane: n-Pentane > Neopentane
- For noble gases: Helium < Argon < Xenon
- For nitrophenols: Meta-nitrophenol > Orthonitrophenol