Which of the following is MOST likely to introduce risk for financial institutions that use blockchain?

Cost of implementation is a financial consideration for a project, not a direct introduction of operational or security risk itself.

Financial institutions require high assurance and regulatory compliance; deploying unproven blockchain applications means introducing technology that lacks extensive real-world testing, established best practices, or robust security audits. This immaturity and unknown behavior can lead to unforeseen vulnerabilities, operational failures, or compliance issues, posing substantial and direct risks.

Disruption to business processes is a potential impact or challenge of any new technology implementation, but it's a consequence rather than the most direct 'introduction' of risk itself.

While any new technology can increase the attack surface, 'implementation of unproven applications' specifically highlights the nature of the application as the primary risk introducer, encompassing vulnerabilities that expand the attack surface.