Which of the following provides the best evidence that a chemical change is taking place?

(A) Steam rises from the surface of a liquid.

(B) A metal object becomes shorter when it is cooled.

(C) A flame burns on the surface of a solid.

(D) A liquid forms as a solid object melts.

Could someone please explain further how I would go aboutfinding the increasing s character of these lone orbital pairs. Anyhelp would be greatly appreciated. Thanks.

I am a little confused here, I had the nuclophile as toluene but it was wrong. Little help on A and B. If you could work the problem so I could see where I am making a mistake it would be greatly appreciated.