Answer is B. Certification to ISO/IEC 27001 is one way to demonstrate to stakeholders and customers that you are committed and able to manage information securely and safely. https://www.iso.org/standard/27001

Answer C: Increases employee education and awareness of security policies An ISMS can improve company culture by promoting a security-conscious environment, and by providing employees with the knowledge and tools necessary to protect the organisation’s information assets https://www.itgovernance.eu/en-ie/isms-benefits-ie

B. Improves customer confidence by demonstrating adherence to best practices. An ISMS is a systematic approach to managing an organization's information security processes and policies. One of its primary objectives is to demonstrate and ensure that the organization follows best practices for information security. By implementing an ISMS, an organization can enhance its security posture, protect sensitive data, and build trust with customers, partners, and stakeholders. Demonstrating adherence to best practices through an ISMS helps increase customer confidence in the organization's commitment to information security.

ISMS definition is C but the question state Benefit of implementing ISMS, then it will be B.