In which pair do both atoms have one electron only in an s orbital in their ground states?
a ca, sc b cu, be c h, he d li, cr
what does electron in ground states means?
and what is the possible answer?

I can help you only with what is electron in ground state. The electron which is not excited or over which no external force is acting that could possibly make it jump to the higher state,is said to be in its ground state.In excited state,the electron has more energy than it normally has. For convenience,suppose you are an electron,you are in Normal mood,but when your little brother snatches the Tv remote from your hand,you become angry.Your normal state is your ground state and your angry state is your excited state.

Ithink is d. physical property