Long term capital gain tax

Dear Shanti

On transfer of Capital Assets attracts capital gain in the year in which such transfer made. There is many exemption to avoide tax liability after fulfilment of certain conditions but

As you mentioned, you have transfered a commercial property and reinvested the same in development of another commercial property not eligible to any exemption under section 54 to 54F of income tax act 1961.

You will have to pay tax on whole sale amount 3.5cr.

If u allraedy been filed income tax return for the AY 2019-10 without mentioning the long term capital gain than it could be attract a penalty in subsequent years for concealment of income under section 271(C) of income tax act 1961 upto 100% to 300% of tax Evaded.

Only last 6 assessment years ka case reopen kar sakta hai AO.

In your case AO assessment year 09-10 ka case reopen nai kar sakega because notic 31.03.2015 tak nai aaya hai...

Prepare back date balance sheet of  AY 09-10 for safety.