Give a test to distinguish butter and cooking oil?

Q. Test that can be used to differentiate between butter and cooking oil is :

Q. Give a test that can be used to differentiate chemically between butter and cooking oil.

Q. Give a test that can be used to differentiable chemically $b/n$ butter and cooking oil.

Q. Bromine water has a red-brown colour due to the presence of bromine in it. A student adds bromine water to a little of cooking oil and butter taken in separate test-tubes.
(a) What will the student observe when he adds bromine water to cooking oil? Give reason for your answer.
​(b) What will the student observe when he adds bromine water to butter? Give reason for your answer.