Which statement best describes a private blockchain?

A private blockchain is defined by its exclusivity, allowing only a select group of participants to access, join, or modify the network. This exclusivity promotes greater control over the data and user permissions, providing a level of confidentiality and privacy not typically available in public blockchains. In this setting, the network is often used by organizations that require a restricted environment for collaboration, transactional activities, or data sharing, ensuring that sensitive information remains protected from unauthorized access.

In contrast, the other options describe characteristics that do not align with the nature of a private blockchain. For instance, the first statement highlights openness, which is a defining feature of public blockchains, rather than private ones. The third option suggests a blockchain operates without a consensus mechanism, which is inaccurate since even private blockchains utilize consensus methods to validate transactions among authorized participants. Lastly, the fourth statement refers to the public ledger format, again associated with public blockchains where anyone can view the transactions, which contradicts the private blockchain's key feature of limited access.