Capital gain is the difference between sale price and the basis (generally purchase price) of the property.
The tax rate depends on the time the property was owned.
If the property is sold in less than a year after purchase - that would be short term capital gain and it is taxed at the regular tax rate.
If the property is sold after it was owned more than a year - that would be long term capital gain and it is taxed at reduced rate - not more than 15%.
That part of long term capital gain which otherwise would be taxed at 15% or less - would have zero percent rate.
Mississippi state income tax for taxable income above $10,000 is 5%
Please let me know if any clarification is needed.