What are the common factors of 36?

It is not possible to give a sensible answer to this question. A common factor refers to a factor that is COMMON to two or more numbers. You have only one number in the question!

There cannot be a common factor of just one number. To be common there need to be at least two numbers. If you find all the factors of two or more numbers, and you find some factors are the same ("common"), then the largest of those common factors is the Greatest Common Factor.

The factors of 36 are 1, 2, 3, 4, 6, 9, 12, 18, 36