Option 1 -> Gautam Buddha was born as Prince Siddhartha Gautama in Lumbini and later attained enlightenment to become Buddha.
Option 2 -> Lord Mahavir was born as Vardhamana, not Siddhartha, and was the 24th Tirthankara of Jainism.
Option 3 -> Emperor Ashoka was the Mauryan emperor known by this name throughout his life, not as Siddhartha.
Option 4 -> Chandra Gupta II was a Gupta dynasty ruler and had no connection to the name Siddhartha.
Hence, Option 1: Gautam Buddha -> Siddhartha was the birth name of Prince Siddhartha Gautama, who renounced his royal life at age 29, attained enlightenment under the Bodhi tree, and became known as Gautam Buddha (the enlightened one) -> correct