Pay tax

Now for filing income tax return online it wont accept such return without payment of income tax.

Yes , if you are liable to pay the taxes and if you do not pay the tax as per the ITR , the return filed by you can become a defective return as per section 139(9) of the income tax act and the AO may give you a chance to rectify the return within 15 days or more as the case may be . The explanation (aa) of this section specifies that if the tax is not paid , it will be treated as defective return and if it is not rectified , it can become invalid return .

If your income tax liability is expected to be more than 10000, you are expected to pay entire tax amount as advance tax on or before 31Mar2015. Else, u will be charged interest. If the amount is lower, pay tax at the time of filing.

Yes.

yes it is mandatory

already answered

Yes. you cannot upload your return if tax is not paid.