Which of the following is a Phenyl Pyrazole?

Fipronil is classified as a Phenyl Pyrazole, which is a type of insecticide known for its potency against a wide range of pests. This class of chemicals acts by inhibiting the insect's central nervous system through the blockade of certain neurotransmitter receptors, particularly the GABA receptors, leading to paralysis and death in targeted insects.

In contrast, the other choices represent different classes of insecticides: Imidacloprid is a Neonicotinoid, targeting nicotinic acetylcholine receptors; Chlorfenapyr is a pyrrole that disrupts ATP production in mitochondria; and Indoxacarb falls into the oxadiazine class, acting by inhibiting sodium channels. Thus, Fipronil's unique chemical structure and mechanism of action as a Phenyl Pyrazole set it apart from these other insecticides.