Which radioactive isotope is most useful for determining the age of mastodont bones found in late Pleistocene sediments?

Carbon-14

Explanation:

Carbon dating is also known as radiocarbon dating. Carbon dating is a technique used in the determination of of age (s) of an object. It has been proved that carbon dating is efficient for dating archaeological specimens and fossils. Carbon dating method was developed by Willard Libby (A physicist).

Carbon-14 is an isotope of of carbon. Carbon-14 is radioactive. Carbon-14 is very important in many aspect both medically (to detect ulcer causing bacteria) and in the determination of age of an object. It is also used in radio labelling.

All living things maintain certain amount of carbon-14 while still alive, but when living things die, the amount of carbon-14 decreases exponentially. Carbon-14 is produced by cosmic radiation in the atmosphere.

Answer: carbon-14

Explanation: the radioactive isotope suitable for dating Pleistocene sediments is Carbon-14