The correct choice is (d) Hydrolysis of acetyl imidazole is an example of this type of catalysis
To elaborate: Hydrolysis of acetyl imidazole is an example of acid base catalysis, and not covalent catalysis. The following statements are true for covalent catalysis:
• A number of coenzymes for covalent adducts generating new electrophilic groups which can function as electron sink.
• These adduct forming coenzymes leads to increase in rate acceleration by route low energy, stabilized, substrate derived carbonions.
• About 100 enzymes show covalent intermediates during catalysis.