**Core Concept**
The concept being tested here is related to the calculation of the concentration of solutions, specifically the number of gram equivalents per liter. It involves understanding the difference between molarity, molality, and equivalent weight.

**Why the Correct Answer is Right**
The correct answer is related to the definition of equivalent weight. One equivalent weight is the mass of a substance that will react with or supply one mole of hydrogen ions (H+) or one mole of electrons. The number of gram equivalents in 1 liter of a solution is calculated by dividing the number of moles of the solute by the equivalent weight of the solute. This is a fundamental concept in chemistry and pharmacology, and is used to calculate the strength of solutions, including those used in medical practice.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not directly related to the definition of equivalent weight.
**Option B:** This option is incorrect because it is related to the definition of molarity, which is the number of moles of solute per liter of solution, not the number of gram equivalents.
**Option C:** This option is incorrect because it is related to the definition of molality, which is the number of moles of solute per kilogram of solvent, not the number of gram equivalents.

**Clinical Pearl / High-Yield Fact**
When calculating the strength of solutions, it is essential to remember that equivalent weight is used to calculate the number of gram equivalents, while molarity and molality are used to calculate the number of moles. This distinction is critical in pharmacology, where the strength of medications is often expressed in terms of their equivalent weight.

**Correct Answer: C. Normality.**