An element ' ' A emits an `alpha`-particle and forms 'B' .'A' and 'B' are

Options

A. Isotopes
B. Isobars
C. Isotones
D. Isodiasphere

Explanation

To solve the problem of identifying the relationship between element 'A' and element 'B' after the emission of an alpha particle, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Alpha Decay**:
- An alpha particle is a helium nucleus, which consists of 2 protons and 2 neutrons. When an element 'A' emits an alpha particle, it loses these particles.

2. **Defining the Initial Properties of Element 'A'**:
- Let the atomic number of element 'A' be \( Z \) and its mass number be \( M \).
- The number of neutrons in element 'A' can be calculated as \( N_A = M - Z \).

3. **Determining the Properties of Element 'B'**:
- After emitting an alpha particle, the atomic number of element 'B' becomes \( Z - 2 \) (since it loses 2 protons).
- The mass number of element 'B' becomes \( M - 4 \) (since it loses 2 protons and 2 neutrons).
- The number of neutrons in element 'B' can be calculated as \( N_B = (M - 4) - (Z - 2) = M - Z - 2 \).

4. **Calculating the Difference in Neutrons and Protons**:
- For element 'A', the difference between the number of neutrons and protons is:
\[ N_A - Z = (M - Z) - Z = M - 2Z \]
- For element 'B', the difference is:
\[ N_B - (Z - 2) = (M - Z - 2) - (Z - 2) = M - 2Z \]

5. **Conclusion**:
- Since both elements 'A' and 'B' have the same difference between the number of neutrons and protons, they are classified as **isodiaphers**.

### Final Answer:
Elements 'A' and 'B' are **isodiaphers**.

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