Step 1: Original interpretation.
Article 21 states that no person shall be deprived of life or personal liberty except according to procedure established by law. Initially, it meant any procedure prescribed by law enacted by a competent legislature.
Step 2: Post-Maneka Gandhi expansion.
Later, the Supreme Court (Maneka Gandhi case, 1978) held that such procedure must also be “just, fair, and reasonable,” bringing it close to “due process of law.”
Step 3: Conclusion.
The literal meaning is option (b), though judicial interpretation expanded its scope.