What determines whether a material melts or burns when heated?

Melting is a change of state. Burning is a chemical reaction (usually with oxygen in the air). What determines whether something melts or burns is whether, as that object heats, it reacts quickly and exothermically with oxygen in the air. As you add thermal energy to a material the individual atom's also gain energy.

Explanation:

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1. a)c-14 has two more protons

2. d)they have different numbers of protons, neutrons, and valence electrons; they are all gases at room temperature.

3. c) iron and nickel.