How is sir converting the bigoh expressions , Which type of identity they are using?

How is sir converting the bigoh expressions , Which type of identity they are using ?
Kindly tell

@Ramitgoel As you know that for m elements, complexity of heap sort is O(m log m). You are given the number of elements that is m in the options. Sir is just substituting each option value into O(m log m) and checking if it is equal to O(log m).

Refer this. This is similar to that question.