Which statement is correct

Options

A. For potassium, the atomic radius `lt` ionic radius, but for bromine, the atomic radius `gt` ionic radius
B. For potassium and bromine both, the atomic radii `gt` ionic radii
C. For potassium and bromine both, the atomic radii `lt` ionic radii
D. For potassium, the atomic radius `gt` ionic radius but for bromine, the atomic radius `lt` ionic radius

Answer

To determine which statement is correct regarding the atomic and ionic radii of potassium (K) and bromine (Br), we need to analyze the properties of these elements and their ions.

### Step-by-Step Solution:

1. **Understanding Atomic Radius**:
- The atomic radius is the distance from the nucleus to the outermost shell of an electron in an atom. It generally increases down a group in the periodic table due to the addition of electron shells.

2. **Potassium (K)**:
- Potassium is an alkali metal located in Group 1 of the periodic table. It has a relatively large atomic radius compared to non-metals.
- When potassium loses an electron to form a potassium ion (K⁺), it loses its outermost electron shell, resulting in a smaller ionic radius compared to its atomic radius.

3. **Bromine (Br)**:
- Bromine is a halogen located in Group 17 of the periodic table. It has a smaller atomic radius than potassium due to its higher nuclear charge and greater effective nuclear charge acting on its valence electrons.
- When bromine gains an electron to form a bromide ion (Br⁻), it increases its electron-electron repulsion, leading to a larger ionic radius compared to its atomic radius.

4. **Comparing Atomic and Ionic Radii**:
- For potassium (K):
- Atomic radius (K) > Ionic radius (K⁺)
- For bromine (Br):
- Atomic radius (Br) < Ionic radius (Br⁻)

5. **Evaluating the Statements**:
- First statement: "For potassium, atomic radius is less than ionic radius." (Incorrect)
- Second statement: "Potassium and bromine both have the same radius." (Incorrect)
- Third statement: "Both potassium and bromine are the same." (Incorrect)
- Fourth statement: "For potassium, atomic radius is greater than ionic radius, and for bromine, atomic radius is less than ionic radius." (Correct)

### Conclusion:
The correct statement is the fourth one: "For potassium, atomic radius is greater than ionic radius, and for bromine, atomic radius is less than ionic radius."