## Core Concept
The Infant Mortality Rate (IMR) is a measure of the number of deaths of infants under one year of age per 1000 live births in a given year. It is an important indicator of the health and well-being of a population. IMR is calculated using the formula: IMR = (Number of infant deaths in a year / Number of live births in the same year) * 1000.

## Why the Correct Answer is Right
To calculate the IMR, we use the given data: the number of infant deaths in a year is 150, and the number of live births in the same year is 3000. Plugging these values into the IMR formula gives us: IMR = (150 / 3000) * 1000 = 50. This means that for every 1000 live births, there are 50 infant deaths. Therefore, the IMR is 50.

## Why Each Wrong Option is Incorrect
**Option A:** This option is incorrect because it does not match our calculated IMR of 50.
**Option B:** This option is incorrect because, similar to Option A, it does not correspond to the IMR calculation we performed.
**Option D:** This option is incorrect as it also does not match the calculated value of 50.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the IMR is a critical indicator of a country's health status and socioeconomic conditions. A high IMR suggests inadequate healthcare, poor sanitation, and possibly a lower standard of living.

## Correct Answer: B. 50