A Life for the Tsar is a  Russian libretto with four acts, Tosca an Italian libretto has how many acts?
Tosca Tosca (] ) is an opera in three acts by Giacomo Puccini to an Italian libretto by Luigi Illica and Giuseppe Giacosa. It premiered at the Teatro Costanzi in Rome on 14 January 1900. The work, based on Victorien Sardou's 1887 French-language dramatic play, "La Tosca", is a melodramatic piece set in Rome in June 1800, with the Kingdom of Naples's control of Rome threatened by Napoleon's invasion of Italy. It contains depictions of torture, murder and suicide, as well as some of Puccini's best-known lyrical arias.
La finta semplice La finta semplice ("The Fake Innocent"), K. 51 (46a) is an opera buffa in three acts for seven voices and orchestra, composed in 1768 by then 12-year-old Wolfgang Amadeus Mozart. Young Mozart and his father Leopold were spending the year in Vienna, where Leopold was trying to establish his son as an opera composer. He was acting on a suggested request from the Emperor Joseph II that the young boy should write an opera.