## Core Concept
Ferrous sulfate is a commonly used iron supplement in the treatment of iron deficiency anemia. It exists in various hydrated forms, with the most common being ferrous sulfate heptahydrate (FeSO4·7H2O). The iron content in ferrous sulfate is crucial for its therapeutic efficacy.

## Why the Correct Answer is Right
Ferrous sulfate heptahydrate (FeSO4·7H2O) has a molecular weight of 278 g/mol, with iron (Fe) having an atomic weight of approximately 56 g/mol. The calculation for the percentage of iron in ferrous sulfate heptahydrate is: (56 / 278) * 100 ≈ 20.1%. This matches option , which indicates that ferrous sulfate contains approximately 20% iron.

## Why Each Wrong Option is Incorrect
* **Option A:** 10% - This is too low compared to the actual iron content in ferrous sulfate.
* **Option B:** 15% - Still lower than the actual iron content.
* **Option D:** 25% - Higher than the calculated iron content in ferrous sulfate heptahydrate.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the elemental iron content is what matters in the treatment of iron deficiency anemia. Different formulations of iron supplements contain varying percentages of elemental iron. For ferrous sulfate, knowing it contains approximately 20% elemental iron is crucial for calculating the dose required to treat anemia effectively.

## Correct Answer: . 20%