Boiling point and melting point of noble gases are in the order

Options

A. `He lt Ne lt Ar lt Kr lt Xe`
B. `He gt Ne gt Kr gt Ar gt Xe`
C. `He lt Kr lt Ne lt Ar lt Xe`
D. `He gt Kr gt Ne gt Ar gt Xe`

Answer

To determine the order of boiling points and melting points of noble gases, we can follow these steps:

### Step 1: List the Noble Gases
The noble gases in order of increasing atomic number are:
- Helium (He)
- Neon (Ne)
- Argon (Ar)
- Krypton (Kr)
- Xenon (Xe)
- Radon (Rn)

### Step 2: Understand the Trend in Properties
As we move down the group of noble gases, the atomic number increases. This increase in atomic number leads to:
- An increase in atomic size.
- An increase in the number of electrons.

### Step 3: Analyze Polarizability
With the increase in atomic size and the number of electrons, the electron cloud around the atom becomes larger. This results in:
- Increased polarizability (the ability of the electron cloud to be distorted).
- Greater Van der Waals forces (also known as London dispersion forces) due to increased polarizability.

### Step 4: Determine the Effect on Boiling and Melting Points
The increase in Van der Waals forces means that more energy (in the form of heat) is required to overcome these forces. Therefore:
- The boiling point and melting point of noble gases increase as we move down the group.

### Step 5: Write the Order of Boiling and Melting Points
Based on the above reasoning, the order of boiling points and melting points from lowest to highest is:
1. Helium (He)
2. Neon (Ne)
3. Argon (Ar)
4. Krypton (Kr)
5. Xenon (Xe)

### Step 6: Conclusion
Thus, the correct order of boiling and melting points of noble gases is:
**He < Ne < Ar < Kr < Xe**

### Step 7: Check the Options
From the options provided in the question, we can confirm that the first option matches our derived order.