The annual festival of the Padmanabhaswamy Temple in Thiruvananthapuram is called:

The correct answer is: A) Alpana Utsavam

Alpana Utsavam is an annual festival held at the Padmanabhaswamy Temple in Thiruvananthapuram, Kerala, India. The festival is celebrated in the month of December and lasts for 10 days. The main attraction of the festival is the alpana, which is a traditional art form of Kerala. Alpana is a form of floor painting that is done using rice flour and natural colors. The alpanas are usually made on the floor of the temple and depict scenes from Hindu mythology.

The other options are incorrect because:

• Thrissur Pooram is an annual festival held at the Vadakkunathan Temple in Thrissur, Kerala, India. The festival is celebrated in the month of April and lasts for 10 days. The main attraction of the festival is the pooram, which is a grand procession of elephants and caparisoned horses.
• Theyyam is a ritualistic dance form that is performed in Kerala, India. Theyyam is performed by men who are possessed by the spirits of gods and goddesses. The dance is accompanied by music and drumming.
• Nishagandhi Festival is a flower festival that is held in Thiruvananthapuram, Kerala, India. The festival is celebrated in the month of February and lasts for 10 days. The main attraction of the festival is the display of flowers and the flower show.