Question

which change is chemical? (1 point)
○ water undergoing electrolysis: liquid water becoming oxygen and hydrogen molecules
○ water evaporating: liquid water becoming gaseous water
○ water boiling: solid water becoming gaseous water
○ water freezing: liquid water becoming solid water

Explanation:

A chemical change involves the formation of new substances, while physical changes only change the state or appearance of a substance.

• For "water evaporating", it's a phase change (liquid to gas) of water, no new substance.
• For "water boiling", note: water boiling is liquid to gas, and solid water (ice) boiling is incorrect; also, it's a physical change.
• For "water freezing", it's liquid to solid (phase change), no new substance.
• For "water undergoing electrolysis", water ($H_2O$) is broken down into hydrogen ($H_2$) and oxygen ($O_2$) molecules, which are new substances. So this is a chemical change.

Answer:

A. water undergoing electrolysis: liquid water becoming oxygen and hydrogen molecules