Q.When does the Court use review powers? What is the difference between judicial review and writ?

The Constitution gives the Supreme Court two distinct tools for protecting the rights of individuals. First, it can issue writs — such as Habeas Corpus or Mandamus — under Article 32, to restore a fundamental right the moment it is violated; High Courts hold the identical power under Article 226. Second, it can declare the offending law itself unconstitutional and therefore inoperative, under Article 13. Together these make the Supreme Court both the protector of citizens' rights and the interpreter of the Constitution.

That second power is judicial review: the authority of the Supreme Court, or a High Court, to strike down any law it finds inconsistent with the Constitution. The phrase "judicial review" never actually appears in the constitutional text — it exists only implicitly, as a natural consequence of India having a written constitution enforceable through a court empowered to invalidate laws that violate Fundamental Rights. Judicial review is not limited to rights cases either: it also lets the Court strike down a law — whether passed by Parliament or a State legislature — that violates the constitutional distribution of powers between the Union and the States, for example if a "Union" law actually trespasses on …