a bright silver and white coloring. similar electron configurations. strong radioactive properties. few or no stable isotopes.
I gave my students this multiple choice question: Strontium, barium, and radium are grouped together on the Periodic Table of the Elements because they all have

Only one answer is correct among these 4 choices:
- a bright silver and white coloring.
- similar electron configurations.
- strong radioactive properties.
- few or no stable isotopes.

Could you tell me which one is correct?

similar electron configurations.