Which type of radiation emitted by radioactive nuclei is the slowest moving and least penetrating?

The type of radiation emitted by radioactive nuclei that is the slowest moving and least penetrating is Alpha radiation.

Here's a step-by-step explanation:

1. Radioactive nuclei can emit three types of radiation: Alpha (α), Beta (β), and Gamma (γ).

2. Alpha particles are made up of two protons and two neutrons, making them the largest of the three types of radiation. This large size contributes to their slow speed and low penetration ability.

3. Because of their large size, alpha particles interact more readily with matter, causing them to slow down and stop more quickly than beta or gamma radiation. This is why they are the least penetrating.

4. In fact, alpha particles can be stopped by a sheet of paper or a few inches of air. They are not capable of penetrating the outer, dead layer of skin on a human body.

5. Therefore, while alpha radiation can be dangerous if ingested or inhaled, it is generally considered less dangerous than beta or gamma radiation due to its lack of penetration ability.