## Core Concept
The problem provides a distribution of forced expiratory volume (FEV) values among 300 smokers, with a median value of 2.5 litres and first and third quartiles (Q1 and Q3) of 1.5 and 4.5 litres, respectively. This data is used to estimate the number of persons with FEV between 1.5 and 4.5 litres.

## Why the Correct Answer is Right
The first quartile (Q1) represents the value below which 25% of the data falls, and the third quartile (Q3) represents the value below which 75% of the data falls. Given that Q1 = 1.5 litres and Q3 = 4.5 litres, this means that 25% of the data points are below 1.5 litres and 25% are above 4.5 litres. Consequently, 50% of the data points lie between 1.5 and 4.5 litres. With a total sample size of 300, the number of persons expected to have an FEV between 1.5 and 4.5 litres is 50% of 300.

## Why Each Wrong Option is Incorrect
- **Option A:** This option suggests a calculation that does not align with the information provided about quartiles and their implications for data distribution.
- **Option B:** Similarly, this option does not correctly reflect the percentage of the sample that would fall between Q1 and Q3.
- **Option D:** This option overestimates the proportion of the sample that falls within the specified range.

## Clinical Pearl / High-Yield Fact
Interquartile range (IQR), which is Q3 - Q1, provides a measure of variability in the middle 50% of the data. Here, IQR = 4.5 - 1.5 = 3 litres. Understanding quartiles and IQR is crucial in clinical research for describing the distribution of health metrics, like FEV, and for identifying potential outliers.

## Correct Answer: B. 150.