Which of the following materials would you use as the metallic core of an electromagnet?

The correct answer is "iron nail".

Explanation:

Electromagnet: It is a temporary magnet. It consists of iron core wounded by the coils and then the current is passed through it.

Then, it will act as a magnet as long as the current is passed through it. When the current flows through it then the electromagnet becomes active.

It loses its magnetism when the power is switched off.

Iron inside the coil makes the magnetic field stronger. It becomes magnetized when the current flows through it. It is used in the electromagnet as it loses its magnetism when the current stops flowing through it.

From the given options in the problem, Only the iron nail can be used as the metallic core of an electromagnet.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.