The question asks about the oldest volcanic formation in India from the provided options. Let's examine each option:

1. Deccan Traps: These are one of the largest volcanic features on Earth, located in west-central India, formed approximately 66 million years ago during the Cretaceous-Paleogene extinction event. Although significant, they are not the oldest.
2. Panjal Traps: Located in the Kashmir region, these volcanic formations are part of the Permian period, formed around 250 million years ago. They are older than the Deccan Traps but not the oldest.
3. Rajmahal Traps: Found in eastern India, these formations date back to the Jurassic period, around 150-160 million years ago. While older than the Deccan Traps, they are not as old as the Dhanjori Volcanics.
4. Dhanjori Volcanics: Dhanjori Volcanics are considered to be among the oldest volcanic formations in India, dating back to the Archean era, approximately 2,500 million years ago.

Given this analysis, the correct answer is Dhanjori Volcanics, as they are the oldest volcanic formation in the provided options.