Final answer:
The year Martin Luther composed and possibly posted his 95 Theses against the sale of indulgences, igniting the Protestant Reformation, was 1517. His intention was to provoke reform within the Catholic Church, but it instead resulted in his excommunication and the rise of Protestant denominations.
Step-by-step explanation:
The critical year in which Martin Luther composed and possibly posted his 95 Theses against the sale of indulgences, sparking the Protestant Reformation, was 1517. This act is traditionally considered to be the beginning of the Reformation, a schism from the Catholic Church leading to the creation of new Christian denominations. The Ninety-five Theses were a direct challenge to the Catholic Church's practice of selling indulgences, which were intended to reduce time in purgatory for the buyer or their loved ones.
Luther's intent was to instigate a discussion within the church for reform. Luther's actions led to a series of events, including his excommunication, that would significantly impact religious and political structures in Europe. His criticism of church practices and the translation of his writings from Latin to German allowed his ideas to spread quickly, thanks largely to the printing press.