Filing of returns

shibin poyilil (TRAINEE) (19 Points)

12 August 2017  
Our retail entity does not have any purchases, sales or any transaction during the month of july, 2017.

is it required to file gst return for that month. if yes, which return is required to be filed? (GSTR-1/2/3/3B)

What is the purpose of filing of GSTR-3B?

Please give me an answer for the above quories..