The ten-day festival culminating in the symbolic immersion of Lord Ganesha idols is:

Attukal Pongala
Makaravilakku
Vinayaka Chaturthi
Thiruvathira

The correct answer is C. Vinayaka Chaturthi.

Vinayaka Chaturthi is a ten-day Hindu festival celebrated in honor of the Hindu god Ganesha. The festival is celebrated in different ways across India, but it typically involves the installation of a Ganesha idol in a home or temple, prayers, and feasting. The festival culminates in the symbolic immersion of the Ganesha idol in a body of water.

Attukal Pongala is a Hindu festival celebrated in Kerala, India. The festival is dedicated to the goddess Parvati and is celebrated by women. The festival involves the preparation of a sweet dish called pongala, which is offered to the goddess.

Makaravilakku is a Hindu festival celebrated in Kerala, India. The festival is dedicated to the sun god Surya and is celebrated on the day of Makar Sankranti. The festival involves the lighting of a lamp on a hilltop and is a major tourist attraction.

Thiruvathira is a Hindu festival celebrated in Kerala, India. The festival is dedicated to the goddess Vishnupriya and is celebrated by women. The festival involves the performance of a dance called Thiruvathirakali.