What is the ltcg tax on debt mf (hold for more than 3 years) for gains less than 1 lakh rupees ?

Is it exempt from LTCG tax ??

NO.

If not what is the tax rate?

20% with indexation....
 

as per this article gains upto 1 Lakh are  tax free and indexation is not allowed for MF.

https://economictimes.indiatimes.com/wealth/tax/understanding-the-new-ltcg-tax-on-equity-and-equity-mutual-fund-units/the-new-ltcg-tax/slideshow/62860584.cms

dhirajlal and nikhil, thanks for your reply