Why are hydrogen bonds the strongest of the intermolecular forces?

a. hydrogen forms covalent bonds
b. hydrogen forms polar bonds
c. hydrogen lacks the protection of inner electron shells
d. hydrogen is protected by four outer electron shells

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.