Which of the following elements is radioactive?

A. magnesium

B. calcium

C. barium

D. radium

Question

Which of the following elements is radioactive?

A. magnesium

B. calcium

C. barium

D. radium

anonymous · Answer

Radium: http://en.wikipedia.org/wiki/Radium The half-life of the most common isotope is 1601 years.

anonymous · Answer

The others may have radioactive isotopes too. Easiest way is to check the Wikipedia pages of the elements and search word "half-life". For example: barium is, in practice, not radioactive, but one could make radioactive isotopes of Barium: http://en.wikipedia.org/wiki/Barium http://en.wikipedia.org/wiki/Isotopes_of_barium The barium you can dig from the ground is not radioactive, because all radioactive isotopes have so short half-lives that they do not exist in earth.

ksaimouli · Answer

barium