Final answer:
The alveoli in fetal lungs are collapsed and filled with fluid before birth. The lungs inflate and expel most of this fluid upon the first breath after birth, aided by pulmonary surfactant. The correct answer is options 1.
Step-by-step explanation:
Before birth, the alveoli in the fetal lungs are collapsed and filled with fluid. This is because, during gestation, the partially collapsed lungs are filled with amniotic fluid and exhibit very little metabolic activity. The first breath typically occurs within 10 seconds after birth, inflating the lungs and expelling most of this fluid. Pulmonary surfactant plays a critical role in the ability of the alveoli to inflate upon the first breath after birth.
Surfactant is an active substance at the air-water interface in the alveoli which reduces lung surface tension. High surface tension arises due to an imbalance in the distribution of molecular forces on water molecules at the air-liquid interface. So,The correct answer is options 1.