In general, metals react by: a. gaining valence electrons b. sharing valence electrons c. sometimes gaining and sometimes losing valence electrons d. losing valence electrons

Option (D) is the correct answer.

Explanation:

It is known that metals are the substances which hold excess number of electrons and hence they need to lose electrons in order to gain stability.

For example, potassium is a metal with atomic number 19 and its electronic configuration is 2, 8, 8, 1.

So, it needs to gain stability and hence, it easily loses its one valence  electron to acquire a positive charge as .

Thus, we can conclude that in general, metals react by losing valence electrons.

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.