**Core Concept**
Polysulphide rubber base impression material is a type of elastomeric impression material used in dentistry for taking precise impressions of the teeth and surrounding tissues. The cross-linking agent is a critical component that facilitates the polymerization reaction, leading to the formation of a stable and durable impression.

**Why the Correct Answer is Right**
The cross-linking agent in polysulphide rubber base impression material is **dimethyl glyoxime**. During the mixing of the material, the base and catalyst are combined, and the dimethyl glyoxime acts as a cross-linking agent, facilitating the polymerization reaction between the base and catalyst. This leads to the formation of a stable and durable impression. The cross-linking reaction is a complex process involving the formation of disulfide bonds between the base and catalyst molecules.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not correspond to the cross-linking agent used in polysulphide rubber base impression material.
**Option B:** This option is incorrect because it is not associated with the cross-linking reaction in polysulphide rubber base impression material.
**Option D:** This option is incorrect because it is not the correct cross-linking agent used in polysulphide rubber base impression material.

**Clinical Pearl / High-Yield Fact**
It is essential to follow proper mixing and storage procedures for polysulphide rubber base impression material to ensure accurate and durable impressions. Improper handling can lead to inferior impressions and compromise the accuracy of dental restorations.

**Correct Answer:** C.