The quantum mechanical model... a
describes electrons as moving through specific circular orbits, and not staying in one place.
b
places electrons in fixed positions, not moving through specific orbits or orbitals.
c
describes electrons as moving anywhere in the atom, not specific circular orbits.
d
describes electrons as moving through cloud-like orbitals, not specific circular orbits.

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.