Availability domains are isolated from each other, fault tolerant, and very unlikely to fail simultaneously or be impacted by the failure of another availability domain. When you configure your cloud services, use multiple availability domains to ensure high availability and to protect against resource failure.
Reference: https://docs.cloud.oracle.com/en-us/iaas/Content/GSG/Concepts/concepts.htm

Explanation
Oracle Data Safe is a unified control center for your Oracle databases which helps you understand the sensitivity of your data, evaluate risks to data, mask sensitive data, implement andmonitor security controls, assess user security, monitor user activity, and address data security compliance requirements.
Whether you're using an Autonomous Database or an Oracle DB system, Oracle Data Safe delivers essential data security capabilities asa service on Oracle Cloud Infrastructure.
Features of Oracle Data Safe:
Oracle Data Safe provides the following set of features for protecting sensitive and regulated data in Oracle Cloud databases, all in a single, easy-to-use management console:
1) Security Assessment helps you assess the security of your cloud database configurations. It analyzes database configurations, user accounts, and security controls, and then reports the findings with recommendations for remediation activities that follow best practices to reduce or mitigate risk.
2) User Assessment helps you assess the security of your database users and identify high risk users. It reviews information about your users in the data dictionary on your target databases, and calculates a risk score for each user. For example, it evaluates the user types, how users are authenticated, the password policies assigned to each user, and how long it has been since each user has changed their password. It also provides a direct link to audit records related to each user. With this information, you can then deploy appropriate security controls and policies.
3) Data Discovery helps you find sensitive data in your cloud databases. You tell Data Discovery what kind of sensitive data to search for, and it inspects the actual data in your database and its data dictionary, and then returns to you a list of sensitive columns. By default, Data Discovery can search for a wide variety of sensitive data pertaining to identification, biographic, IT, financial, healthcare, employment, and academic information.
4) Data Masking provides a way for you to mask sensitive data so that the data is safe for non-production purposes. For example, organizations often need to create copies of their production data to support development and test activities. Simply copying the production data exposes sensitive data to new users. To avoid a security risk, you can use Data Masking to replace the sensitive data with realistic, but fictitious data.
5) Activity Auditing lets you audit user activity on your databases so you can monitor database usage and be alerted of unusual database activities.

Explanation
Archive storage is the most cost effective for archive data