Isomers are defined as:. i. atoms with the same number of protons but different numbers of neutrons.
ii. atoms with the same number of protons but different numbers of neutrons.
iii. molecules with different chemical formulas but similar biological functions.
iv. molecules with the same general three-dimensional structures but different chemical formulas.
v. elements with the same number of electrons in the outer shell.
vi. molecules with the same chemical formula but different structures.