Capital gain

Yes You have to paid because Exemption allowed regarding Residential House and not Business Property

Yes, capital gains arise from sale of property and deductions are given on purchase of certain other properties , after fulfilling all terms and conditions. Here, in your case , sale of vacant land will attract capital gains( long term if held for more than 3 years otherwise short term capital gain). You will have to deduct cost of acquisition( indexed, if applicable) from the selling price and resultant will be your capital gains on which you will be taxed.  No deduction is available for purchase of commercial property here.