Explanation
Regardless of the particular cloud service used, physical security of hardware and facilities is always the sole responsibility of the cloud provider. The cloud provider may release information about their physical security policies and procedures to ensure any particular requirements of potential customers will meet their regulatory obligations. Personal security of developers and regulatory compliance are always the responsibility of the cloud customer. Responsibility for operating systems, and the auditing of them, will differ based on the cloud service category used.

Explanation
A data custodian is responsible for the safe custody, transport, and storage of data, and the implementation of business roles.

Explanation
WAFs detect how the application interacts with the environment, so they are optimal for detecting and refuting things like SQL injection and XSS. Password cracking, syn floods, and ransomware usually aren't taking place in the same way as injection and XSS, and they are better addressed with controls at the router and through the use of HIDS, NIDS, and antimalware tools.