Assertion (A) : o-Phenol sulphonic acid on heating at `100^(@)C` changes to p-phenol sulphonic acid.
Reason (R) : Sulphonation of phenol is a reversible process.
A. Both A and R are true and R is the correct explanation of A.
B. Both A and R are true and R is not a correct explanation of A.
C. A is true but R is false.
D. A is false but R is true.