Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.

Question: Salts of weak acids or bases can affect the acidity or what of their aqueous solution? Answer: basicity
Salts of weak acids or bases can affect the acidity or basicity of their aqueous solutions.

Question: The outer layer of what anatomical structure is so tough that it keeps out most pathogens? Answer: skin
This drawing shows that the skin has many layers. The outer layer is so tough that it keeps out most pathogens.

Question: What happens between particles with opposite charges? Answer: they attract
When charged particles are close enough to exert force on each other, their electric fields interact. Particles with opposite charges attract each other. Particles with like charges repel each other.