1) they have similar chemical properties.
for example fluorine from the 17th column is a non metal so does all the elements of that group.
2)they have same valence electrons in their outermost shell
example
electronic configuration of
hydrogen 1, lithium 2,1, sodium 2,8,1 and so on.
3) have same valency.
I think that the correct answer is reactants of photosynthesis.
Organelles.
balalalallallalalalalallalalallalalala, this answer is right.
