Read the sentence. Ouch, that frying pan is very hot! Which word in the sentence is an interjection?

An interjection expresses an a sudden remark. "Ouch" is the interjection.

in the sentence "Ouch, that frying pan is very hot!" OUCH, is an interjection,

The interjection is a part of speech which is generally employed in informal language than in formal writing or speech. Basically, the purpose of using interjections is to express emotions in an abrupt and exclamatory way. They can convey a wide variety of emotions such as: excitement, joy, surprise, or disgust. They express meaning or feeling in a word or two.