**Core Concept**
The standard error of the mean (SEM) is a measure of the variability or dispersion of a sample mean from the true population mean. It is an essential concept in statistics, particularly in clinical research and epidemiology. In this context, the SEM is used to estimate the reliability of the sample mean Hb (hemoglobin) value in a population of pregnant females.

**Why the Correct Answer is Right**
The standard error is calculated using the formula: SEM = σ / √n, where σ is the standard deviation of the population and n is the sample size. Given that the standard deviation of Hb is 1 gm% and the sample size is 100 women, the SEM can be calculated as follows: SEM = 1 gm% / √100 = 1 gm% / 10 = 0.1 gm%. This represents the expected variability of the sample mean Hb value from the true population mean.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, so we will skip it.
**Option B:** This option is also not provided, so we will skip it.
**Option C:** This option is also not provided, so we will skip it.

**Clinical Pearl / High-Yield Fact**
When calculating the standard error of the mean, it's essential to remember that a smaller sample size will result in a larger SEM, indicating greater variability of the sample mean from the true population mean.

**Correct Answer: A. 0.1 gm%.**