Which question cannot be asked when discussing a customer's loan application?

The question that cannot be asked when discussing a customer's loan application is related to their marital status, as it can lead to potential discrimination under the Equal Credit Opportunity Act (ECOA). This law prohibits lenders from making credit decisions based on race, color, religion, national origin, sex, marital status, or age, as well as the receipt of public assistance. Inquiries about marital status can inadvertently introduce bias into the lending process and do not have a direct correlation with the applicant's ability to repay the loan.

On the other hand, questions regarding income, employment status, and credit score are crucial for assessing a borrower's financial stability and creditworthiness. These factors help lenders make informed decisions, as they directly relate to the applicant’s ability to fulfill the obligations of the loan repayment.