`alpha`-particle consists of

Options

A. 2 protons only
B. 2 protons and 2 neutrons only
C. 2 electrons, 2 protons and 2 neutrons
D. 2 electrons and 4 protons only

Explanation

To determine what an alpha particle consists of, we can analyze the components of an alpha particle step by step.

### Step-by-Step Solution:

1. **Understanding the Alpha Particle**:
An alpha particle is a type of nuclear particle that is emitted during certain types of radioactive decay, specifically alpha decay.

2. **Comparison with Helium Atom**:
An alpha particle is essentially the same as a helium nucleus. A helium atom consists of:
- 2 protons
- 2 neutrons
- 2 electrons

3. **Charge of the Alpha Particle**:
The alpha particle has a +2 charge because it does not contain any electrons. Therefore, it consists only of the positively charged protons and neutrons.

4. **Identifying the Components**:
Since the alpha particle is derived from a helium nucleus, it contains:
- 2 protons (which contribute to the positive charge)
- 2 neutrons (which are neutral and contribute to the mass)

5. **Conclusion**:
Thus, the composition of an alpha particle is:
- 2 protons and 2 neutrons only.

Based on the options provided in the question, the correct answer is **B: two protons and two neutrons only**.