Question

1. which of the following elements has the smallest atomic radius? a) na b) al c) cl d) k 2. as you move left to right across a period, the atomic radius: a) increases b) decreases c) stays the same d) first increases, then decreases

Explanation:

Step1: Recall atomic - radius trend

Atomic radius decreases across a period from left to right and increases down a group.

Step2: Analyze elements in question

Na, Al, and Cl are in the same period (Period 3), and K is in Period 4. Since K is in a lower - period, it has a larger atomic radius than the others. Among Na, Al, and Cl, Cl is the right - most element in the period. So, Cl has the smallest atomic radius among the given elements.

Step3: Recall periodic trend for second question

As you move left to right across a period, the number of protons increases while the electrons are added to the same energy level. The increased nuclear charge pulls the electrons closer, so the atomic radius decreases.

Answer:

1. C. Cl
2. B. Decreases