The element having no neutron in the nucleus of its atom is-
(a). hydrogen
(b). nitrogen
(c). helium
(d). boron

Options

A. H
B. Mg
C. He
D. Ag

Answer

To determine which element has no neutrons in its nucleus, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Atomic Structure**:
- An atom consists of protons, neutrons, and electrons. The number of protons is equal to the atomic number, and the number of neutrons can be calculated using the formula:
\[ \text{Number of Neutrons} = \text{Atomic Mass} - \text{Atomic Number} \]

2. **Analyzing Each Option**:
- **(a) Hydrogen**:
- Atomic Mass = 1
- Atomic Number = 1
- Number of Neutrons = 1 - 1 = 0
- **Conclusion**: Hydrogen has 0 neutrons.

- **(b) Nitrogen**:
- Atomic Mass = 14
- Atomic Number = 7
- Number of Neutrons = 14 - 7 = 7
- **Conclusion**: Nitrogen has 7 neutrons.

- **(c) Helium**:
- Atomic Mass = 4
- Atomic Number = 2
- Number of Neutrons = 4 - 2 = 2
- **Conclusion**: Helium has 2 neutrons.

- **(d) Boron**:
- Atomic Mass = 11
- Atomic Number = 5
- Number of Neutrons = 11 - 5 = 6
- **Conclusion**: Boron has 6 neutrons.

3. **Final Conclusion**:
- Among the options analyzed, only hydrogen has no neutrons in its nucleus.

### Answer:
The element having no neutron in the nucleus of its atom is **(a) hydrogen**.

---