1: The Establishment Clause prohibits the government from establishing or favoring any religion. The Lemon Test, derived from Lemon v.
Kurtzman, sets criteria for determining if a law violates the Establishment Clause: it must have a secular purpose, not advance or inhibit religion, and avoid excessive entanglement with religion.

2:Yes, burning the US flag is protected by the First Amendment.
Texas v. Johnson (1989)
established that flag burning is a form of symbolic speech, protected under the First Amendment’s free speech clause.

3:Saying “I’m taking the Fifth” means invoking the Fifth Amendment of the US Constitution, which protects individuals from self-incrimination.
It allows a person to refuse to answer questions in a legal proceeding if the answers could incriminate them.