Ionic radii `"________"` with increases in atomic number in a period
and `"_______"` in a group.

Explanation

To answer the question regarding the trends in ionic radii, we can break it down into two parts: the trend in a period and the trend in a group.

### Step-by-Step Solution:

1. **Understanding Ionic Radii in a Period:**
- As we move from left to right across a period in the periodic table, the atomic number increases. This means that the number of protons in the nucleus increases, which leads to a higher effective nuclear charge.
- The increased effective nuclear charge pulls the electrons closer to the nucleus, resulting in a decrease in the size of the ions. Therefore, the ionic radii **decrease** as we move across a period.

2. **Understanding Ionic Radii in a Group:**
- When we move down a group in the periodic table, we are adding additional principal quantum shells (energy levels) for the electrons.
- Each new shell is further away from the nucleus, which increases the distance between the nucleus and the outermost electrons. This results in an increase in the size of the ions. Therefore, the ionic radii **increase** as we move down a group.

### Final Answer:
- Ionic radii **decrease** with increases in atomic number in a period and **increase** in a group.