Final answer:
An acceleration clause in a mortgage instrument allows a lender to require the borrower to pay the entire remaining balance of the loan immediately in the event of default.
Step-by-step explanation:
An acceleration clause in a mortgage instrument allows a lender to require the borrower to pay the entire remaining balance of the loan immediately in the event of default.
This means that if the borrower fails to make their mortgage payments as agreed, the lender has the right to demand full repayment of the loan.