Question

the main purpose of requiring a cosigner on a loan is to
limit a lenders collateral requirement
limit a borrowers capacity requirement
secure the loan if the lead borrower defaults.
expand a banks lending capacity.

Explanation:

A cosigner is someone who agrees to take on the responsibility of repaying a loan if the primary borrower defaults. This provides an extra layer of security for the lender. It is not about limiting collateral requirements, limiting borrower capacity requirements, or expanding a bank's lending capacity.

Answer:

secure the loan if the lead borrower defaults.