21. Which of the following is true about ionic radius?1 pointdecrease going down a groupdecrease across a period for metalsincrease across a period for nonmetalsbigger than atomic radius for metalssmaller than atomic radius for nonmetals

The following are true about ionic radius:

1. Increase going down a group: As we move down a group in the periodic table, the number of energy levels increases, which means the ionic radius increases.

2. Decrease across a period for metals: As we move across a period from left to right, the number of protons in the nucleus increases, pulling the electrons closer to the nucleus and decreasing the ionic radius.

3. Increase across a period for nonmetals: This is not generally true. The ionic radius usually decreases across a period for both metals and nonmetals due to increasing nuclear charge.

4. Bigger than atomic radius for metals: This is not generally true. When a metal loses electrons to form a cation, the ionic radius is usually smaller than the atomic radius because the electron cloud shrinks due to the loss of electrons.

5. Smaller than atomic radius for nonmetals: This is generally true. When a nonmetal gains electrons to form an anion, the ionic radius is usually larger than the atomic radius because the electron cloud expands due to the addition of electrons.