Why might the pattern of reactivity between the alkali metals be useful to scientists?

To show trends based on the  number of electrons around the atom. In this case, having one extra election makes them prone to donating and thus  getting rid of the election to reach stability

Explanation:

this has been asked like 4 times

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.