Final answer:
The statement that A) a change in color often occurs during a chemical change is correct.
Step-by-step explanation:
The correct statement about physical and chemical changes is: a. A change in color often occurs during a chemical change.
This is true because a chemical change involves a substance being transformed into a different substance with different properties, which may include a different color. For example, when iron rusts, it changes from gray to an orange-brown color.
Choices b, c, and d are incorrect: b. A change of state of matter does not always indicate a chemical change; it can be a physical change, like water turning to ice. c. A lack of visible color change doesn't ensure a process is chemical, as some chemical changes do not involve a color change. d. A process that doesn't involve a change of state may still be a chemical change; for instance, colorless hydrogen gas reacts with colorless oxygen gas to form water without changing state.
It's crucial to remember that physical changes, such as changing states of matter, do not change the composition of the substance, whereas chemical changes create new substances with different properties.