Assertion (A) is true because pancreatitis is, by definition, the inflammation of the pancreatic tissue (parenchyma).
Reason (R) is also true — the main mechanism for injury in acute pancreatitis is the premature activation of digestive enzymes like trypsin within the pancreas.
These activated enzymes cause the pancreas to digest itself, which is known as autodigestion.
This mechanism directly explains the inflammation described in (A).
Therefore, both the Assertion and the Reason are true, and (R) correctly explains (A).
So, option (1) is the correct answer.