The correct answer is **A. Assignments**.
In Azure AD, the Assignments section of a device configuration profile determines which users, devices, or groups the profile applies to. If you want Profile1 to apply to Device1 only, you should modify the Assignments of Profile1 to include only Device1. The other options (Settings, Scope (Tags), and Applicability Rules) do not directly control which devices a profile applies to.
Please note that this will only work if Device1 and Device2 are not in the same Azure AD group that Profile1 is assigned to. If they are, you might need to create a new group for Device1 and assign the profile to that group.