Which of the following actinides are found naturally on Earth?

• A. Uranium, thorium, and protactinium
• B. Neptunium, americium, and curium
• C. Uranium, thorium, and plutonium
• D. Plutonium, californium, and berkelium

Answer: (A)

Verified step by step guidance

1. Understand that actinides are a series of elements from atomic numbers 89 (actinium) to 103 (lawrencium), many of which are radioactive and some are synthetic.
2. Recall that naturally occurring actinides on Earth are primarily those with relatively long half-lives and are found in the Earth's crust due to their stability over geological time.
3. Identify that uranium (U), thorium (Th), and protactinium (Pa) are naturally occurring actinides because they have isotopes with long half-lives and are found in nature.
4. Recognize that elements like neptunium (Np), americium (Am), curium (Cm), plutonium (Pu), californium (Cf), and berkelium (Bk) are mostly synthetic or found only in trace amounts due to their short half-lives and are not considered naturally abundant.
5. Conclude that the correct set of naturally occurring actinides on Earth is uranium, thorium, and protactinium.