Form 15g/h

Whether 15G/H can be filed by a Non-resident and claim exemption from tds. pls suggest the law and section and guide us with explanation where it actually exempts 15G/H to a non-resident

In the present law there is no tax on NRE a/c but there is tax on NRO a/c. my question is when both are non-resident accounts (NRE and NRO) why NRO a/c is suffered to tax pls suggest.

My friend says if there is an agreement betweeen countries the tax to be deducted (TDS) is only 10% and not 30% pls suggest. How can I find such agreements.