Nri holding a ordinary saving bank account

HI

An Indian origin person, now an NRI and a foreign citizen is having a ordinary bank account in India, where his rent income is being credited. 

1. Can a foreign citizen (POI) hold a ordinary bank account in India?  What are the consequences?

2. Can he convert the said account to NRO and still get the rent income credited in this account?

3.  Where can he deposit the rental income?

4.  Does he have to link his adhar card with the bank accounts, as he doesnt have adhar card and does not intend to return to India in the near future.

Please advice on the above

Regards

Christie Alex