**Core Concept**
Total space analysis by Merrifield is a method used in peptide synthesis to determine the efficiency of a reaction by analyzing the space occupied by the reactants and products. This technique involves measuring the volume of the reaction mixture before and after the reaction, allowing for the calculation of the amount of product formed.

**Why the Correct Answer is Right**
The Merrifield resin used in this analysis has a fixed volume, which remains constant throughout the reaction. By measuring the volume of the reaction mixture before and after the addition of the reagent, the amount of product formed can be calculated. This is based on the principle of volumetric analysis, where the volume of the reaction mixture is directly proportional to the amount of product formed.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the principle behind total space analysis by Merrifield. While it may involve a resin, it does not involve measuring the volume of the reaction mixture.
**Option B:** This option is incorrect because it does not accurately describe the method used in total space analysis by Merrifield. While it may involve a reaction, it does not involve measuring the volume of the reaction mixture.

**Clinical Pearl / High-Yield Fact**
Total space analysis by Merrifield is a useful technique for optimizing peptide synthesis reactions, allowing for the efficient production of high-quality peptides.

**Correct Answer:** C. Merrifield resin.