The harvest festival celebrated across Kerala with flower arrangements, feasts, and cultural activities is:

Onam
Vishu
Makar Sankranti
Shivaratri

The correct answer is A) Onam.

Onam is a 10-day harvest festival celebrated in the Indian state of Kerala. It is one of the most important festivals in Kerala and is a time for family reunions and feasting. The festival is also a time for cultural activities, such as boat races, music and dance performances, and art exhibitions.

Onam is believed to have originated in the 12th century and is associated with the legend of King Mahabali. According to the legend, King Mahabali was a benevolent ruler who was loved by his people. However, he was also very powerful and this made the gods jealous. The gods decided to send Vishnu, one of the most important gods in Hinduism, to defeat Mahabali. Vishnu took on the form of a dwarf named Vamana and challenged Mahabali to give him as much land as he could cover in three steps. Mahabali agreed and Vamana began to walk. With his first step, Vamana covered the earth. With his second step, he covered the heavens. With his third step, Vamana asked Mahabali to give him his head. Mahabali agreed and Vamana pushed him down to the underworld. However, Mahabali was allowed to visit his kingdom once a year, during the festival of Onam.

Onam is celebrated with great pomp and show. People decorate their houses with flowers and rangolis (a type of floor decoration made from rice flour). They also wear new clothes and visit temples. The main event of the festival is the Onam feast, which is a lavish meal that is shared with family and friends. The feast includes traditional Kerala dishes such as appam (a type of pancake), idiyappam (a type of string hoppers), and sambar (a lentil and vegetable stew).

Onam is a time for joy and celebration. It is a time to remember the legend of King Mahabali and to celebrate the harvest. It is also a time to come together with family and friends and enjoy the rich culture of Kerala.