this is an MCQ for my upcoming exam. I have searched the internet but found mixed answers so far.
The resistance is defined as pressure difference per flow (basically just an application of Ohm's law).
So if the alveoli diameter is reduced to half (resulting in a halved radius), as the resistance changes by the fourth, it is increased by factor 16 (24).
Note: As the bronchioles terminales are connected parallel, they actually do only make up roughly 20% versus 40% for the other bronchioli and 40% for the upper airways.
Source: Pape H, Kurtz A, Silbernagl S, ed. 9., Physiologie 2019. doi:10.1055/b-006-163285