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

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

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.