Why are the alkali metals and the halogens very reactive

Answer in explanation

Explanation:

The reactivity or passiveness of an element depends solely on how close it is to attain a noble gas configuration. This means the closer an element is to attain a noble gas configuration, the greater its reactivity in both direction, positively or negatively.

Alkali metals belong to group 1 of the periodic table while halogens belong to group 17 of the periodic table. This means they are just one electron away from achieving the stability of a noble gas configuration. While alkali metals need to lose one electron to form a univalent positive ion, halogens news to gain one electron to form a univalent negative ion.

They tend to go about this vigorously and as such undergo several chemical reactions because of that single electron they neeed.

the answer is 0.42 is that is an option. this question provides no info

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.