Which is most useful tracer isotope? a) carbon-14 (b) strontium-90 (c) cobalt-60 (d) iodine-131?

different isotopes for different purposes. carbon 14 is used in carbon dating. strontium- 90 and cobalt 60 for radiation therapy and I-131 for thyroid. so it all depends on how you intend to use the isotope.