Step 1: Mechanism overview:
Fats with double bonds react with air oxygen. Light and heat start the reaction by making radicals.
Step 2: Steps:
Initiation forms a lipid radical. Propagation passes the radical from one molecule to the next with oxygen. Termination joins two radicals.
Step 3: Answer:
A chain of radical steps is the signature of a free radical chain reaction, option (C).
Final Answer:
The mechanism is a free radical chain reaction.
\[ \boxed{\text{(C) }\text{free radical chain reaction}} \]