Compare the number of valence electrons for each to whether or not they donate or receive electrons

Valency electrons is the number outermost electron present in atom of an element . The valency electron of an atom determines the kind of bonding an element undergoes. The valency electrons determines whether an atom of element will either donate electrons or receive electrons.

Explanation:

Valency electrons is the number outermost electron present in atom of an element . The valency electron of an atom determines the kind of bonding an element undergoes. The valency electrons determines whether an atom of element will either donate electrons or receive electrons.

Elements donates  or receive electron to attain or fulfill the octet rule and this account for the stability. Most metallic elements donates electrons and because they have few valency electrons , this also contributes to their ability to loose electrons easily . Metallic elements like sodium, magnesium, calcium etc loose electrons during bonding with other non metals. When metals loose electrons they form cations

Non metallic element have high number of valency electron and they tend to receive electrons from metallic elements to attain stability . When they gain electron they form anions.  

An example of bonding that involves donating and receiving are bonding between Na and Cl atoms to form NaCl . The metallic sodium loose one electron while the chlorine atom gains one electron to attain the octet rule.

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.