Alpha particles are

Options

A. `2` free protons
B. helium atoms
C. singly ionised helium atoms
D. doubly ionised helium atoms

Answer

To answer the question "Alpha particles are:", we need to understand what alpha particles are in the context of nuclear physics. Here’s a step-by-step breakdown of the solution:

### Step 1: Definition of Alpha Particles
Alpha particles are a type of nuclear particle that is emitted during radioactive decay. They are composed of two protons and two neutrons.

**Hint:** Remember that alpha particles are related to the nucleus of an atom and consist of specific subatomic particles.

### Step 2: Composition of Alpha Particles
Alpha particles can be represented as \( ^4_2He \), which indicates that they have a mass number of 4 (2 protons + 2 neutrons) and an atomic number of 2 (which corresponds to helium).

**Hint:** The notation \( ^A_ZX \) is useful to understand the mass number (A) and atomic number (Z) of particles.

### Step 3: Identification of Alpha Particles
Given the options in the question, we can identify that alpha particles are essentially doubly ionized helium atoms. This is because they have lost two electrons (due to their positive charge) and consist of the nucleus of a helium atom.

**Hint:** Consider how ionization affects the charge of an atom and what it means for an atom to be ionized.

### Step 4: Conclusion
Based on the above information, we conclude that alpha particles are best described as "doubly ionized helium atoms."

**Hint:** Always cross-check your understanding of terms like "ionized" and "particles" to ensure clarity in definitions.

### Final Answer
Alpha particles are doubly ionized helium atoms.