Answer:
This pair of molecules are cyclopentane and pentane.
Step-by-step explanation:
For both structures, the black balls are Carbon atoms and the white balls are hydrogen atoms. Every Carbon atoms could attach four other atoms, and every Hydrogen atoms could attach only one atom. Thus, the first one is a cycle of five carbon atoms, in which every carbon is attached to the other two carbons and also to two atoms of hydrogen. This molecule is called cyclopentane.
The second one is a linear molecule, because the balls are connected successively. In which the ends two atoms of carbon have attached three atoms of hydrogen and the three intermediate carbons have attached two atoms of hydrogen. This molecule is called pentane.