Final answer:
The Reign of Terror was the worst part of the French Revolution, characterized by extreme violence and widespread executions.
Step-by-step explanation:
The worst part of the French Revolution was the period known as the Reign of Terror, which occurred from 1793 to 1794. The Reign of Terror was characterized by extreme violence and the execution of perceived enemies of the revolutionary government. During this time, the guillotine was used extensively and around 40,000 people were executed, including King Louis XVI and Queen Marie Antoinette.