Question

How are isotopos defined?

forms of different elements that have the same number of neutrons in each atom
forms of different elements that have the same number of protons in each atom
forms of the same element that differ in the number of neutrons in each atom
forms of the same element that differ in the number of protons in each atom

Answer 1

isotopes are atoms that have the same number of protons and electrons but different numbers of neutrons and therefore have different physical properties.