Question 3. 3.when the candle was lighted, it melted into liquid and became Solid again after few seconds or in a minute. what causes these changes?

I. presence of heat
III. absence of heat
II. presence of oxygen
IV. absence of oxygen
A. I, II and III
B. I and IV
C. I and II
D. all of above

A. I,II and III

Explanation:

Let's describe the situation in a simplified way.

First remember, in ambient temperature, the candle is in solid form.

As you light the candle, the region of the candle near the flame suffers an increase in energy, caused by the heat of the flame. As you know, when we give enough heat to a solid, it will change of phase, from solid to liquid, and this is why the candle melts. Now, this change of phase is due to the heat of the flame, so when the liquid phase is away from the flame (because the flame went out, or because the liquid wax fell and now is far from the flame) the wax will cool down, and return to the solid phase.

Then we must have:

Presence of heat to go from solid to liquid.

Absence of heat to go from liquid to solid.

And we have a flame, then we must have presence of oxygen.

Then the correct option is:

A. I,II and III

what is the question because that is not a question.