INCOME TAX ON OCI STATUS

If your client plan to stay in India permently then submit application for Indian Citizenship.

Your OCI status will be changed to normal citizen. 

Or if he want to continue as OCI, No need follow any procedure just file your tax return as NRI.

Tax implications : 

You have to pay tax on your Income from

1) salary

2) Housing Property

3) Business & Professional

4)  Capital Gains (Short & Long term)

5) Other Sources

As you said your client earns income from Salary. You have to file ITR-1 only for salary.

And your second question, he wishes to sell his small flat to his family member. 

To avail exemption, Donee should be blood relative, spouse, children, Parents so on.

THANKS ALL FOR YOUR REPONSE APPRICATE YOUR TIME 

OCI = Foreigner.

Even if the name suggests overseas citizen, he will be exactly equal to a foreigner who is a tax resident of India.