Answer: D) forming mixtures from pure substances.
Step-by-step explanation
Entropy is the measure of randomness or disorder of a system. If a system moves from an ordered arrangement to a disordered arrangement, the entropy is said to decrease and vice versa.
a) Increase in temperature of a gas: As increasing the temperature , increases the kinetic energy of molecules , the molecules move faster and thus entropy increases.
b) Melting a solid : The randomness will increase as liquids move freely as compared to solids and hence entropy will also increase.
c) chemical reactions that increase the number of moles of gas: As more gaseous molecules will be formed, more will be the randomness and hence entropy increases.
d) forming mixtures from pure substances: As substances in a mixture do not react chemically and thus the molecules remain same and entropy remain same.
e) decreasing the volume of a gas: According to Boyle's law, decreasing the volume will increase the pressure and thus entropy will increase.