Which isotope is known to have the longest half-life?

The isotope known to have the longest half-life among the choices provided is Carbon-14. Carbon-14 has a half-life of approximately 5,730 years, making it significantly longer-lived than the other isotopes listed.

Cobalt-60, Cesium-137, and Iridium-192 all have much shorter half-lives. For instance, Cobalt-60 has a half-life of about 5.27 years, Cesium-137 about 30 years, and Iridium-192 approximately 74 days.

This extended half-life of Carbon-14 allows it to be used effectively in radiocarbon dating, which is a critical tool in archaeology and geology for determining the age of organic materials. The longevity of Carbon-14 makes it especially valuable for dating items that are thousands of years old, as it remains detectable and can provide accurate age estimates well beyond the time frames suitable for the other isotopes listed.