7. Which of the following is always true when a substance undergoes a phase change? *
O A. The molecules keep moving at the same average speed.
B. The substance becomes a liquid as it heats up.
C. The melting point of the substance changes.
D. The substance is made up of the same type of molecules.

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answer; i do believe the correct answer is (river); /// good luck

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.