Which festival is celebrated after the month of Ramzan?

The correct option is Eid ul Fitr.

Explanation:
Ramzan (also known as Ramadan) is the ninth month of the Islamic lunar calendar, during which Muslims worldwide observe a month of fasting, prayer, reflection, and community.
The festival celebrated immediately after the conclusion of the month of Ramzan, on the first day of the following month (Shawwal), is Eid ul Fitr (often called the "Festival of Breaking the Fast"). It marks the end of fasting and is celebrated with special morning prayers, charitable giving, feasting, and festivities with family and friends.