In which of the following cases, the Supreme Court of India declared section 303 of the Indian Penal Code (which mandates the award of death sentence to life imprisonment, if he commits murder) unconstitutional?

In Mithu vs State of Punjab, a five-Judge Bench of the SC struck down Section 303 of the IPC, holding that the provision violated Articles 14 and 21 of the Constitution. As per Section 303, if a person undergoing life imprisonment committed murder, they would mandatorily be sentenced to death. The SC held that the provision drew an arbitrary distinction between persons committing murder and persons undergoing life imprisonment who committed murder. There was no rationale behind this distinction. Further, a mandatory death sentence prevents courts from exercising their discretion.