Protection Philosophy

No.

YES.

It works, but that is not the question in real life.

It depends, what is the agreed upon procedure in your state.

As someone who has actually helped design and build a portable substation for powering an islanded section of the grid I would say it depends on what you mean by 'protection'.

Yes the grid islanding relay (likely) has other protection functionality built-in and being used for island-mode protection (with or without island-mode transfer).

The question is a little too broad except to say yes it can be, but it depends on how it is being used.

Thnx for reply, but what exactly I want to know is as differential scheme is unit protection, Can grid islanding be considered as unit protection?

Given the limited information provided and a quick internet search the answer is (likely) yes. An islanded system of the grid can be considered a discrete zone and hence must rely on its own protection.

Does this help? Is this a homework question?

It was just a discussion and I actually wanted to have a point with justification.

Thank you by the way.