## Core Concept
The problem involves understanding the distribution of a pulmonary function test parameter, specifically the Forced Expiratory Volume (FEV), in a population of smokers. The FEV is a critical measure in respiratory medicine, reflecting the lung's ability to expel air quickly. The question provides a median value and the first and third quartiles (Q1 and Q3) of FEV in a sample of 300 smokers.

## Why the Correct Answer is Right
The first quartile (Q1) is 1.5 litres, and the third quartile (Q3) is 4.5 litres. By definition, Q1 is the value below which 25% of the data points fall, and Q3 is the value below which 75% of the data points fall. Therefore, the interquartile range (IQR), which spans from Q1 to Q3, contains the middle 50% of the data. Given that the total sample size is 300, 50% of the sample would be 150 individuals. Thus, it is expected that 150 persons in the sample have an FEV between 1.5 and 4.5 litres.

## Why Each Wrong Option is Incorrect
**Option A:** This option suggests 75 individuals, which would correspond to 25% of the sample (since 25% of 300 is 75), not the 50% that falls between Q1 and Q3.
**Option B:** This option suggests 225 individuals, which corresponds to 75% of the sample (since 75% of 300 is 225), exceeding the proportion expected between Q1 and Q3.
**Option D:** This option suggests 300 individuals, implying the entire sample falls within this range, which is not accurate since Q1 and Q3 define the range for only the middle 50% of the data.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the interquartile range (IQR) is a measure of variability that describes the range of the middle 50% of values in a dataset when it is ordered from smallest to largest. This concept is crucial in understanding the distribution of pulmonary function tests like FEV in clinical and research settings.

## Correct Answer Line
**Correct Answer: C. 150.**