Alpha rays emitted from a radioactive substance are

Options

A. negatively charged particles
B. ionised hydrogen nuclei
C. doubly ionised helium atom
D. uncharged particles having the mass equal to proton

Explanation

To solve the question regarding the nature of alpha rays emitted from a radioactive substance, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Alpha Rays**:
- Alpha rays are a type of radiation emitted during radioactive decay. They consist of particles known as alpha particles.

2. **Composition of Alpha Particles**:
- An alpha particle is made up of 2 protons and 2 neutrons. This composition is identical to that of a helium nucleus.

3. **Ionization State**:
- When an alpha particle is emitted, it carries a positive charge due to the presence of 2 protons. This means it is a positively charged particle.

4. **Identifying the Helium Atom**:
- A neutral helium atom has 2 protons and 2 neutrons, with 2 electrons to balance the charge. When an alpha particle is emitted, it is essentially a helium nucleus without its electrons, making it a doubly ionized helium atom (He²⁺).

5. **Conclusion**:
- Therefore, the correct answer to the question is that alpha rays emitted from a radioactive substance are indeed **doubly ionized helium atoms**.

### Final Answer:
The correct option is C: **Doubly ionized helium atom**.

---