. The age of a rock sample can be determined byen
finding the relative amount of a parent isotope
that has changed into a daughter isotope within
the sample. Which property of radioactive decay
allows the age of the rock to be determined in
years?

The half-life.

Explanation:

The half-life is  the  amount of time that the radioactive elements takes to decay so that half its original mass is left.

This rate is constant for a particular radioactive isotope. For example the half-life of Uranium-238 is 4.47 billion years.

1. they vary with a higher number because boiling is way hotter than melting