**Core Concept**
Infant Mortality Rate (IMR) is a crucial public health indicator that measures the number of deaths per 1000 live births in the first year of life. It is a key metric for assessing the quality of healthcare and living conditions in a given population.

**Why the Correct Answer is Right**
To calculate IMR, we use the formula: IMR = (Number of infant deaths in a year / Number of live births in a year) x 1000. In this case, the number of infant deaths is 150 and the number of live births is 3000. Plugging these values into the formula gives us: IMR = (150 / 3000) x 1000 = 50.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option would incorrectly use the total population (100000) instead of the number of live births, leading to an incorrect calculation.
* **Option B:** This option would incorrectly use the number of infant deaths (150) as the numerator and the total population (100000) as the denominator, resulting in a completely incorrect calculation.
* **Option C:** This option is not provided, but if it were, it would likely be an incorrect calculation or a distractor.

**Clinical Pearl / High-Yield Fact**
To remember the IMR formula, simply recall that you need to divide the number of infant deaths by the number of live births and then multiply by 1000 to get the rate per 1000 live births.

**Correct Answer: A. IMR is 50 per 1000 live births.**