Question

which unstable element is used to determine the age of volcanic rock?
argon
carbon - 12
potassium
carbon - 14

Explanation:

Potassium - argon dating is a common method for dating volcanic rocks. Potassium - 40 is an unstable isotope. When potassium - 40 decays, it can turn into argon - 40. By measuring the ratio of potassium - 40 to argon - 40 in a volcanic rock sample, the age of the rock can be determined. Carbon - 12 is a stable isotope. Carbon - 14 dating is mainly used for dating organic materials (such as fossils of once - living organisms) and is not suitable for volcanic rocks as volcanic rocks are inorganic. Argon alone (as a stable gas in the atmosphere) is not the unstable element used for the initial dating process; it is the product of the decay of potassium - 40 in the potassium - argon dating method.

Answer:

potassium