To determine the taxability of penalty amount received from the builder, you will have to answer one question, whether this purchase of commercial property was for investment purpose or
for the purpose of trading in property. I presume that this was purchased for investment purposes to derive rental income from leasing of the said property. In such a case the penalty amount received from the builder is a capital receipt and not liable to tax as income and you may claim exemption from incom tax and receive refurn. But if you are engaged in business of buying and selling of properties then such amount received is business income liable to tax.