Is Matter Around Us Pure

Assertion: Oxygen is an element.
Reason: It cannot be decomposed by a physical or a chemical process.

Directions: In the question given below, there are two statements labelled as Assertion (A) and Reason (R). Mark your answer as per the codes provided below:

A. Both A and R are true and R is the correct explanation of A.
B. Both A and R are true but R is not the correct explanation of A.
C. A is true but R is false.
D. A is false but R is true.
E. Both A and R are false.