Gallium melting into its liquid form at 30°C is an example of a:

• A. irreversible change
• B. physical change
• C. chemical change
• D. nuclear change

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the definitions of the types of changes. A physical change involves a change in the state or appearance of a substance without altering its chemical composition.
2. Step 2: Recognize that melting is a phase change where a solid turns into a liquid due to temperature increase, but the substance's chemical identity remains the same.
3. Step 3: Identify that an irreversible change means the change cannot be undone, while melting is typically reversible by cooling the liquid back to solid.
4. Step 4: Note that a chemical change involves forming new substances with different chemical properties, which does not happen during melting.
5. Step 5: Conclude that since gallium melting at 30°C changes only its physical state and is reversible, it is an example of a physical change.