Public Read-Only is the correct Lead OWD because it balances duplicate prevention with ownership-based editing. Users can see existing Lead records across the organization, which helps them identify whether a prospect already exists before creating another Lead, but they cannot edit another user ' s Lead merely because they can view it. A Private OWD would protect ownership more strictly but would undermine the duplicate-reduction objective because users might not be able to discover Leads owned elsewhere. Public Read/Write/Transfer would go too far in the opposite direction by allowing broader modification or reassignment than the requirement permits. The organization can complement the OWD with Duplicate Rules and Matching Rules for stronger prevention and warning behavior, but the OWD still establishes the right record-visibility baseline. Study Guide reference: Access to Records - Lead OWD, Public Read-Only, record ownership, duplicate prevention, and least-privilege access. The implementation should also be validated with representative users so effective permissions, sharing inheritance, and any cross-object access behave exactly as designed before production release.