Which of the following statements regarding the variation of atomic radii in the periodic table is true?

Options

A. In a group,these is continuous decrease in size with icrease in atomic number.
B. The size of inert gases is larger than halogens.
C. The size of inert gases is smaller than halogens.
D. In `3^(rd)` period, the size of atoms increase with increase in atomic number.

Explanation

To determine which statement regarding the variation of atomic radii in the periodic table is true, we need to analyze the trends of atomic radii as we move across periods and down groups in the periodic table.

### Step-by-Step Solution:

1. **Understanding Atomic Radius**:
- The atomic radius is defined as the distance from the nucleus to the outermost shell of electrons.

2. **Trend Down a Group**:
- As we move down a group in the periodic table, the atomic radius increases. This is because with each successive element, an additional electron shell is added, which increases the size of the atom.

3. **Trend Across a Period**:
- As we move from left to right across a period, the atomic radius decreases. This occurs because the number of protons in the nucleus increases, which leads to a higher effective nuclear charge. The electrons are added to the same shell, and the increased nuclear charge pulls the electrons closer to the nucleus, resulting in a smaller atomic radius.

4. **Evaluating Statements**:
- **Statement A**: "In a group, there is a continuous decrease in size with an increase in atomic number."
- This is false; atomic size increases down a group.
- **Statement B**: "The size of inert gases is larger than halogens."
- This is true; noble gases have completely filled electron shells, leading to larger atomic sizes due to increased inter-electronic repulsion.
- **Statement C**: "In the third period, the size of the atom increases with an increase in atomic number."
- This is false; atomic size decreases across a period.
- **Statement D**: "The size of the inert gases is larger than halogens."
- This is true; as explained above.

5. **Conclusion**:
- The true statement regarding the variation of atomic radii in the periodic table is that the size of inert gases is larger than halogens.

### Final Answer:
The true statement is: "The size of inert gases is larger than halogens."