Point out the idiomatic sentences.
a. Exploiting the employees has now become a fun and game in the so called modern Educational Institutes.
b. Most of the inexperienced ministers act under the thumb of the secretaries in the Ministry.
c. Insecticides and pesticides can never be made null and void even though we wash vegetables repeatedly.
d. Mahatma Gandhi was very shy and trembling when he made his maiden speech.
Answer options:

The correct answer is Option D (All of these).

Key Points:
• Sentence a contains 'fun and games' (frivolous activity/amusement).
• Sentence b contains 'under the thumb of' (completely under the control/influence of someone).
• Sentence c contains 'null and void' (having no legal force or validity/ineffective).
• Sentence d contains 'maiden speech' (the first speech made by a person).
• Option 4 (All of these).
• All four sentences incorporate recognized idiomatic phrases ('fun and games', 'under the thumb', 'null and void', and 'maiden speech'). Hence, all of them are idiomatic sentences.
• Key Takeaway: Sentences containing 'fun and games', 'under the thumb', 'null and void', and 'maiden speech' are all idiomatic.