Which of these is an example of tyrannicide?
Tyrannicide is the killing or assassination of a tyrant or unjust ruler, purportedly for the common good. In the Classical period, tyrannicide had even been legally permitted, and encouraged.
Thus, out of the given incidents, only one can be called a tyrannicide: The death of Julius Caesar.
Julius Caesar, the Roman dictator, was assassinated by a group of senators on 15th March of 44 BC during a meeting of the Senate at the Curia of Pompey of the Theatre of Pompey in Rome, after been stabbed 23 times by the senators. The senators claimed to be acting over fears that Caesar's unprecedented concentration of power during his dictatorship was undermining the Roman Republic, and presented the deed as an act of tyrannicide. At least 60 senators were party to the conspiracy, led by Marcus Junius Brutus and Gaius Cassius Longinus.