If you got all tangled up on this question like me:

anatomic dead space= conducting airways

Alveolar dead space= alveoli that are ventilated but not perfused (wiki)

physiologic dead space=anatomic dead space+ alveolar dead space

Po2: just no

Good memory tip: to remember dead space, think "dead people don't have any blood flow"--> lung areas that are NOT perfused

In this case, the lung region is well perfused. So the answer must be shunt.

bnb video - ventilation and perfussion.
underventilated but well perfused = aspiration, mucus plug, atelectasis. this causes physiologic shunting.