Correct order of b.p.t is /are:

Options

A. `H_(2)ltHe`
B. `H_(2)ltD_(2)`
C. `H_(2)OltD_(2)O`
D. `NH_(3)ltSbH_(3)`

Answer

To determine the correct order of boiling points among the given options, we need to analyze the boiling points based on molecular weight and the strength of intermolecular forces. Here’s a step-by-step breakdown:

### Step 1: Analyze the first option - Boiling point of H2 < He
- **Explanation**: Hydrogen (H2) is a diatomic molecule with strong covalent bonds, while helium (He) is a monoatomic noble gas with weak Van der Waals forces. Due to the stronger intermolecular forces in H2, its boiling point is higher than that of He.
- **Conclusion**: This statement is **incorrect**.

### Step 2: Analyze the second option - Boiling point of H2 < D2
- **Explanation**: Deuterium (D2) is an isotope of hydrogen and has a greater molecular weight (D2 = 4 amu vs. H2 = 2 amu). Higher molecular weight generally leads to a higher boiling point due to stronger London dispersion forces.
- **Conclusion**: This statement is **correct**.

### Step 3: Analyze the third option - Boiling point of H2O < D2O
- **Explanation**: D2O (heavy water) has a greater molecular weight than H2O (water). The increased mass leads to stronger hydrogen bonding and higher boiling point.
- **Conclusion**: This statement is **correct**.

### Step 4: Analyze the fourth option - Boiling point of NH3 < SbH3
- **Explanation**: Antimony trihydride (SbH3) has a greater molecular weight than ammonia (NH3). As we move down the group in the periodic table, the boiling points of hydrides increase due to increased molecular weight and van der Waals forces.
- **Conclusion**: This statement is **correct**.

### Final Conclusion:
- The correct orders of boiling points are:
- Option 2: H2 < D2 (Correct)
- Option 3: H2O < D2O (Correct)
- Option 4: NH3 < SbH3 (Correct)
- Therefore, the only incorrect order is from Option 1 (H2 < He).

### Summary of Correct Options:
- The correct orders of boiling points are **2, 3, and 4**.

---