A measure of the average kinetic energy of the particles in an object is called

Your question is not clear but if you can explain yourself i would be glad to .  just trying to : ))

Idon't mean to be a smart alec, length of atoms' bonds is the simplest way to define it.

Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.