Fill in the blanks with an appropriate verb form:

Ram was watching TV when I ……………………… for my exam.

was preparing

The correct verb form to fill in the blank is was preparing. The past progressive tense of the verb "prepare" is was preparing. The context of the sentence indicates that the speaker was preparing for the exam in the past while Ram was watching TV, so the past progressive tense is the most appropriate tense to use.

The other options are incorrect.

• Prepared is the simple past tense of the verb "prepare".
• Had prepared is the past perfect tense of the verb "prepare".
• Would be preparing is the future perfect progressive tense of the verb "prepare".