Option A is correct: The Hallisalasya painting, found on the outer wall of the continuous verandah connecting Caves 4 (known as the Rang Mahal) and 5 of the Bagh Caves in Madhya Pradesh, depicts a joyous folk dance. The mural vividly portrays a ring of female dancers keeping time by striking small wooden sticks together, highly reminiscent of the modern Dandiya or Garba. They are accompanied by female musicians playing instruments such as the hand-drum (hudukka) and small cymbals (kamsyatalas). It is highly valued by historians for its detailed depiction of ancient central Indian social life.

Option B is incorrect: Although the Bagh Caves are ancient rock-cut Buddhist viharas dating back to the 5th–6th century CE (Gupta period), the Hallisalasya painting is a secular scene depicting social life, not a depiction of the Buddha in a meditative pose.

Option C is incorrect: The depiction of Shiva and Parvati on Mount Kailasha is a famous theme in Hindu cave architecture (such as at Ellora or Elephanta), but it is not the subject of the Hallisalasya mural in the Buddhist Bagh Caves.

Option D is incorrect: Samudramanthan (Churning of the Ocean) is a prominent Hindu mythological event depicted in various temples and sculptures, but it is not represented in the Hallisalasya painting.

Therefore, Option A is the correct answer.