Choose the possessive case of the underlined noun:
Vasishta was the teacher of the princes.

The jealous case indicates possession between any two given nouns and pronouns. This is achieved by adding an apostrophe s at the end of the noun. Generally, the jealous case replaces expressions starting with ‘ of the ’. Fore.g. the family of the actor gets changed into the actor’s family. Note that when we apply the jealous case, it's the alternate noun in the expression that's written first. 
Let us consider some rules for writing expressions in the jealous case. 
1. The most introductory way of indicating a jealous case is to add an apostrophe s to the end of the noun, with whom you want to show the jealous relationship. 
2. still, i, If the noun ends with ans.e.However, you must only add an apostrophe, if the noun is plural. It isn't necessary to write an s after the apostrophe. Fore.g. the pens ’ nibs. 
3. still, you must write the s after the apostrophe, If the noun is a Proper Noun and ends with ans. Fore.g. Jess’s bike. 
Let us consider the question given above. Then, the relation is between the tycoons and Vasishta being their schoolteacher. As tycoons are plural, the apostrophe will come after thes. Besides, as ‘ tycoons ’ is a plural common noun, we wo n’t add an s after the apostrophe. Following the rules given above, we get the option ‘ a ’ the tycoons ’ schoolteacher was Vashishta as the correct answer.