Is it excessive to say "Are you sure you want to…"?

The situation: In our application there're several actions once done that will cause the data loss or won't be able to be undone. So, we ask users whether they are sure of what they are doing before completing the action.

Which way to ask this is better?

I'm a bit lost here. The first option seems a bit excessive but the second one in its turn seems a bit abrupt.

Which style should I follow? Maybe you have some better suggestions?

Examples: 1) Are you sure you want to delete this task? You will not be able to undo this action.

2) Delete this task? You will not be able to undo this action.

Buttons: delete cancel

1) Are you sure you want to delete this post? You will not be able to undo this action.

2) Delete this post? You will not be able to undo this action.

Buttons: delete cancel

1) Are you sure you want to undo this activity? You will not be able to undo this action.

2) Undo this activity? You will not be able to undo this action.

Buttons: undo cancel

P.S. visually it would seem like what facebook has: Are you sure you...?

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