Explanation:

According to the Microsoft SC-300: Microsoft Identity and Access Administrator Study Guide and official Microsoft Learn documentation ("Manage and use custom security attributes in Microsoft Entra ID"), custom security attributes allow administrators to define key-value pairs that can be applied to various Microsoft Entra objects. These attributes can be used for fine-grained access control, app governance, and conditional policies.
Who can create custom security attributes:
Custom security attributes can only be created and managed by users assigned either of these roles:
* Global Administrator
* Attribute Definition Administrator
The Security Administrator role does not have the permissions required to create or modify attribute schema definitions.
Hence, from the table:
* User1 (Global Administrator) #
* User2 (Attribute Definition Administrator) #
* User3 (Security Administrator) #
Therefore, User1 and User2 only can create custom security attributes.
To which identities can custom security attributes be assigned:
As per Microsoft documentation:
"Custom security attributes can be assigned to supported Microsoft Entra objects, including users, groups, service principals, and managed identities." This means attributes can be attached to:
* Group objects (Group1) #
* Managed identities (MI1) #
* Service principals (Service1) #
Thus, the correct assignable identities are Group1, MI1, and Service1 only.