Which statement about protons is true? a. they have a charge that is always a whole number. b. they are smaller than neutrons and electrons. c. they weigh much less than electrons. d. they are inherently unstable.

Quantum mechanics applies to subatomic, atomic, nanometer-size, and micrometer-size systems. nanometer, micrometer, and kilometer-size systems. atomic, nanometer-size, and micrometer-size systems. subatomic, atomic, and nanometer-size systems.