The atomic number and the mass number of an atom remains unchanged when it emits

Options

A. gamma ray
B. a neutron
C. `beta-` particle
D. An `alpha-` particle

Answer

To solve the question regarding which type of emission keeps both the atomic number and mass number of an atom unchanged, we can analyze each option provided. Here's a step-by-step solution:

### Step 1: Understand the definitions
- **Atomic Number (Z)**: The number of protons in the nucleus of an atom, which defines the element.
- **Mass Number (A)**: The total number of protons and neutrons in the nucleus of an atom.

### Step 2: Analyze the emissions
1. **Gamma Ray Emission**:
- Gamma rays are high-energy electromagnetic radiation.
- They have no mass and no charge.
- **Effect**: When an atom emits a gamma ray, it does not change its atomic number or mass number.

2. **Neutron Emission**:
- A neutron is a neutral particle with a mass of approximately 1 atomic mass unit.
- **Effect**: When an atom emits a neutron, the mass number decreases by 1 (A - 1), while the atomic number remains unchanged (Z).

3. **Beta Particle Emission**:
- A beta particle is an electron (or positron) emitted from a nucleus.
- **Effect**: When an atom emits a beta particle, the atomic number increases (Z + 1) or decreases (Z - 1) depending on whether it is a beta minus or beta plus decay, but the mass number remains unchanged (A).

4. **Alpha Particle Emission**:
- An alpha particle consists of 2 protons and 2 neutrons (essentially a helium nucleus).
- **Effect**: When an atom emits an alpha particle, both the atomic number and mass number change (Z - 2, A - 4).

### Step 3: Conclusion
From the analysis:
- The only emission that does not change the atomic number or mass number is **gamma ray emission**.

### Final Answer
The atomic number and the mass number of an atom remain unchanged when it emits a **gamma ray**.

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