Final answer:
option a,Grinding pepper is an example of a physical change because only the appearance of the pepper is altered, not its chemical composition.
Step-by-step explanation:
Grinding pepper is an example of a physical change. A physical change is where the form or appearance of matter changes, but not its composition. When grinding pepper, the size and shape of the pepper grains are altered, but the chemical identity and the composition of the pepper itself remain the same. No new substances are formed during this process, unlike some of the other options like burning a candle or converting hydrogen and oxygen to water which are chemical changes. These involve a change in composition and result in new substances.
Other examples of physical changes include the condensation of steam and the dissolving of sugar in water, whereas burning gasoline, souring of milk, and a nail rusting are examples of chemical changes. Physical changes are usually reversible, and the substance can often be returned to its original state.