Capital Gain Tax on Resale of underconstruction Property

Hello Sir, I had booked an apartment in Feb 2010 and entered into the "Apartments Buyer Agreement" with the builder. In next 3 years I made the payment for 95% of the purchase value as per the builder’s payment plan. This property is delayed and expected possession is in Oct 2015 . I am seeking advice on the capital gains on the sale of this property and wanted to know if the registration date in Oct 2015 has a bearing the taxability of profit on when to Sell that is before or after registration. Scenario1: Selling the property Immediately After registration in Oct 2015 Q1: Since the original sale deed was executed 5 years back, can the profit be taxed under the Long term capital gains even though the Registration and actual possession date is the current year ? Q2. Can I use the CPI indexation from 2010 to 2015 for calculating the capital Gains ? Q3. Which date “Apartments Buyer Agreement date” or the “registration date “ is considered for determination of Capital gains and the Indexation calculation? Ruchir