Which characteristic of potassium makes it useful for dating rocks?

• A. It forms colorful compounds that are easy to detect.
• B. It has a radioactive isotope, K-40, that decays at a known rate.
• C. It is highly reactive with oxygen in the atmosphere.
• D. It is abundant in all types of rocks.

Answer: (B)

Verified step by step guidance

1. Understand that the question is about why potassium is useful in dating rocks, which relates to the method of radiometric dating in geology.
2. Recall that radiometric dating relies on the presence of radioactive isotopes that decay over time at a known, constant rate, allowing scientists to determine the age of rocks.
3. Identify that potassium has a radioactive isotope, potassium-40 (K-40), which decays into argon-40 and calcium-40, making it useful for dating geological samples.
4. Recognize that the key characteristic making potassium useful for dating rocks is the presence of this radioactive isotope with a known half-life, not its reactivity or abundance.
5. Conclude that the correct reason is that potassium contains the radioactive isotope K-40, which decays at a known rate, enabling accurate age determination of rocks.