What is the Latin word for king?

a. fasces

b. rex

c. res publica

d. patrician

it is rex?

The latin word for king is rex - b.

When you read old texts you can observe that certain people (who were kings) were also given this name which implied they were kings. You could for example find "Oedipus rex" which means Oediupus the king, this is also how we know (a way at least) what this meant.