The highest summit of the Nilgiri Hills is called Doda-betta. Doda-betta is a mountain peak located in the Western Ghats of Tamil Nadu, India.
Let`s examine the other options to understand why they are not the correct answer:
Option 1: Coonoor-betta - Coonoor-betta is not the highest summit of the Nilgiri Hills. Coonoor-betta is a small hill located near the town of Coonoor but it is not the highest peak in the region.
Option 2: Anaimudi - Anaimudi is the highest peak in South India, but it is not part of the Nilgiri Hills. Anaimudi is actually located in the neighbouring state of Kerala in the Western Ghats.
Option 4: Vellangiri - Vellangiri is also not the highest summit of the Nilgiri Hills. Vellangiri, also known as SonaGiri, is a range of hills located in the Namakkal district of Tamil Nadu.
In conclusion, the correct answer is option 3, Doda-betta.