UTGST is applicable when:

The other options are incorrect because:

• Option A is incorrect because UTGST is not applicable when goods are sold from a union territory to a state. This is because the supply of goods from a union territory to a state is an inter-state supply, and inter-state supplies are subject to IGST.
• Option B is incorrect because UTGST is not applicable when goods are purchased by the central government. This is because the central government is not a taxable person under GST.
• Option D is incorrect because UTGST is not applicable when there is an interstate supply. This is because interstate supplies are subject to IGST.

I hope this helps! Let me know if you have any other questions.