Which of the following is a clause in property and casualty contracts that broadens coverage without an additional premium?

The correct answer is liberalization, which is a clause found in property and casualty insurance contracts designed to broaden coverage without requiring the insured to pay an additional premium. This clause ensures that if the insurer adopts a new law, rule, or endorsement that expands coverage after the policy has been issued, that broader coverage automatically applies to existing policies. The intent is to protect policyholders from losing out on enhancements to the policy that could occur after their contract has been finalized, which enhances customer satisfaction and loyalty.

Understanding the other options provides further clarity on their distinct roles. The assignment clause typically pertains to the transfer of rights or benefits of the policy to another party, which does not necessarily broaden coverage. A binder is a temporary agreement that provides proof of insurance until the formal policy is issued, but it does not expand coverage. Coinsurance is a provision that requires the insured to maintain a certain level of coverage to avoid penalties in the event of a claim; it is more about compliance with policy terms than expanding benefits. Thus, liberalization stands out as the specific mechanism that directly broadens the coverage aspect of property and casualty contracts without extra cost.