Final answer:
Mark would recognize a gain of $300,000 on the sale of his business's retail building, calculated as the selling price ($500,000) minus the adjusted basis ($200,000). The transaction's payment method does not affect the recognized gain in the year of the sale.
Step-by-step explanation:
Mark would recognize gain of $300,000 in the year of the sale of his retail building. The gain is calculated as the difference between the selling price of the asset ($500,000) and its adjusted basis ($200,000).
While the buyer is offering to pay with $150,000 in cash and a promissory note for the remaining $350,000, the entire $500,000 counts towards the amount realized on the sale in the year of the sale. The installment agreement does not change the total gain recognized, but it would affect when Mark reports the income for tax purposes. Given that the question did not specify treating this as an installment sale, we are calculating the gain in the year of sale.