The answer is number 1 - energy is emitted
Energy is released when an atom in an excited state returns to the ground state.
i may be wrong but Use the normal boiling points: propane, C3H8, –42.1˚C; butane, C4H10, –0.5˚C; pentane, C5H12, 36.1˚C; hexane, C6H14, 68.7˚C; heptane, C7H16, 98.4˚C; to estimate the normal boiling point of octane, C8H18.
Answer: (3) ppm
Explanation: Concentration is defined as the amount of solute dissolved in a known amount of the solvent or a solution.
Parts per million (ppm) is used to express the concentration when a very small quantity of solute is present in a large quantity of the solution. It is defined as the mass of solute present in one milion
parts by mass of the solution.

L/s is used to express flow rate.
J/g is used to express energy per unit mass.
kPa is used to express pressure.
Explanation:
I can't guess it properly
Answer:
B. chemical
Explanation:
Chemical change cannot go back to its original form