The purpose of his speech was to lampoon the leading politicians of the day.

Answer: Option C

Praise : express warm approval or admiration of.
Expose : make (something) visible by uncovering it.
Ridicule : the subjection of someone or something to contemptuous and dismissive language or behaviour.
Defame : damage the good reputation of (someone); slander or libel.
Lampoon : publicly criticize (someone or something) by using ridicule, irony, or sarcasm.

Synonym of Lampoon is Ridicule