Explanation:

- Mahavir Jayanti is an important religious holiday in Jainism. It celebrates the birth of Lord Mahavir, the 24th and last Tirthankara.

- The festival usually falls in March or April, according to the lunar calendar. Based on the Gregorian calendar, it's most often celebrated in April.

Option 1: May

- May is typically not the month when Mahavir Jayanti is celebrated.

Option 2: April

- This is the usual month when Mahavir Jayanti is observed.

Option 3: September

- September does not align with the traditional timing of Mahavir Jayanti.

Option 4: December

- December is also not the correct month for Mahavir Jayanti.