Isotope of which noble gas is isotonic (same number of neutrons) with Tritium? 

Options

A. a. Ne
B. b. He
C. c. Kr
D. d. Rn

Answer

To solve the question of which isotope of a noble gas is isotonic (has the same number of neutrons) with Tritium, we can follow these steps:

### Step-by-Step Solution:

1. **Identify Tritium**:
Tritium is a hydrogen isotope represented as \( ^3H \) or \( _1^3H \). Here, the superscript (3) indicates the total number of nucleons (protons + neutrons), and the subscript (1) indicates the number of protons.

2. **Calculate the Number of Neutrons in Tritium**:
The number of neutrons can be calculated using the formula:
\[ \text{Number of Neutrons} = \text{Total Nucleons} - \text{Number of Protons} \]
For Tritium:
\[ \text{Number of Neutrons} = 3 - 1 = 2 \]

3. **Identify Noble Gases**:
The noble gases include Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn).

4. **Check Isotonic Noble Gas Isotopes**:
We need to find a noble gas isotope that has the same number of neutrons (2) as Tritium.
- Helium has isotopes such as \( ^4He \) (which has 2 neutrons).
- Neon has isotopes like \( ^20Ne \) (which has 10 neutrons).
- Argon has isotopes like \( ^40Ar \) (which has 22 neutrons).
- Krypton has isotopes like \( ^84Kr \) (which has 48 neutrons).
- Xenon has isotopes like \( ^132Xe \) (which has 78 neutrons).
- Radon has isotopes like \( ^222Rn \) (which has 136 neutrons).

5. **Conclusion**:
The only noble gas isotope that has 2 neutrons is Helium (\( ^4He \)). Therefore, the isotope of the noble gas that is isotonic with Tritium is Helium.

### Final Answer:
The isotope of the noble gas that is isotonic with Tritium is Helium (\( ^4He \)).

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