Final answer:
A lecithin/sphingomyelin (L/S) ratio that reflects fetal lung maturity is approximately 2.5; thus, option c. 2:1 is the correct answer which most closely indicates mature fetal lungs.
Step-by-step explanation:
The measurement of lecithin in relation to sphingomyelin is used to assess fetal lung maturity, known as the lecithin/sphingomyelin (L/S) ratio. A ratio which reflects fetal maturity of the lungs is typically approximately 2.5. According to the information provided, a mature fetal lung L/S ratio is around 2.5, low risk is indicated by ratios between 2.4 and 1.6, while a high risk of infant respiratory distress syndrome (IRDS) is associated with ratios less than 1.5. Therefore, among the options presented, the one most reflective of fetal lung maturity would be c. 2:1. Lesser ratios could indicate insufficient surfactant levels, leading to the collapse of the alveoli and difficulty breathing, characteristic of IRDS.