Question

which phrase describes one characteristic of radioactive elements?
a are produced in a laboratory
b decay at a constant rate
c have a constant number of particles
d release energy and particles to maintain radioactivity

Explanation:

Radioactive elements decay at a constant rate (half - life). Not all are produced in a laboratory (some occur naturally). They do not have a constant number of particles as they decay. And they release energy and particles as they decay, not to maintain radioactivity (radioactivity is due to their unstable nuclei).

Answer:

B. decay at a constant rate