The correct answer is:
The sentence which accurately uses the homophones "it's" or "its" is:
- As far as I know, it's starting right after school.
Homophones are words which are pronounced the same, but differ in meaning and sometimes spelling too, as in this case.
The word It's, is always short for It is (or it has, in informal speech). In the sentence chosen as accurately written it means it is (It's) starting right after school.
The word Its, is a possessive pronoun; means belonging to it.
Therefore, the first sentence should have said: "its bone"; the second sentence: "It's going to be"; and, the last sentence: its charger.