You are provided with three watch glasses containing milk, petrol and mustard oil, respectively

You are provided with three watch glasses containing milk, petrol and mustard oil, respectively. Suppose you bring a burning candle near these materials one by one, which material(s) will catch fire instantly and why?

Answer:
Petrol will catch fire instantly because it is highly inflammable. Mustard oil and milk has very high ignition temperature. So, they will not catch fire instantly.