There is no such thing as dual nationality in India.
The nearest you can get are:
PIO (Person of Indian Origin) Link
Any person:
1. who at any time held an Indian passport; or
2. he/she or either of his/her parents or grandparents or great grandparents was born in and permanently resident in India as defined in the Government of India Act, 1935 and other territories that became part of India thereafter provided neither was at any time a citizen of any country as may be specified by the Central Government from time to time; or
3. who is a spouse of a citizen of India or a Person of Indian Origin as mentioned above.
The scheme is broad-based, covers up to four generations and also the foreign spouse of a citizen of India or a PIO.
OCI (Overseas Citizen of India) Link
Persons of Indian Origin, who migrated from India after 26 January, 1950, and
1. who were citizens of India on or at anytime after 26.01.1950 or
2. who were eligible to become Indian citizens on 26th January, 1950 or
3. belonged to a territory that became part of India after 15th August, 1947 and
4. their children and grand children,
whose present nationality is such that the country of nationality allows dual citizenship in some form or the other under the local laws, will be eligible to be registered as OCI.
I hope this helps.