Potassium-40 (K-40) decays into argon-40 (Ar-40). Which of the following are true statements? Select all that apply.

A. K-40 is the parent, and Ar-40 is the daughter.
B. Ar-40 is the parent, and K-40 is the daughter.
C. A rock sample containing a relatively small amount of Ar-40 is old.
D. A rock sample containing a relatively small amount of Ar-40 is young.

The correct answers are options A. "K-40 is the parent, and Ar-40 is the daughter" and D. "A rock sample containing a relatively small amount of Ar-40 is young".

Explanation:

Potassium-40 (K-40) is a radioactive isotope that decays into argon-40 (Ar-40) with a really long half-life of 1.251 billion years. Since K-40 is the one that produces Ar-40, K-40 is considered the parent isotope and Ar-40 is considered the daughter isotope. This phenomenon is used to date rocks, known as the potassium–argon dating approach. A rock sample containing a relatively small amount of Ar-40 is young, because K-40 takes a long time to decay and the more Ar-40 is in the rock the more time has passed since the rock was created.