Okay, let's tackle this question. The user is asking about a procedure that induces cross-linking in the polymerization of linear acrylic chains. Hmm, I need to recall the polymer chemistry involved in acrylic materials, especially in dentistry. Acrylics are commonly used in dental prosthetics, like dentures.

So, polymerization of acrylics typically involves linear chains. To make them stronger, cross-linking is necessary. Cross-linking agents form covalent bonds between the polymer chains, creating a three-dimensional network. This increases the material's rigidity and resistance to deformation.

Wait, what are the common cross-linking agents for acrylics? I think it's something like methyl methacrylate (MMA) and maybe a cross-linker like ethylene glycol dimethacrylate (EGDMA). But how does the polymerization process work? The question is about the procedure, not the agent. So the procedure might involve adding a cross-linking agent during the polymerization process.

The options aren't provided, but common procedures could include using a specific catalyst, a certain temperature, or adding a cross-linking agent. Let me think. In dental acrylics, the common method is to use a combination of MMA and a cross-linker like EGDMA. The cross-linker has two methacrylate groups, allowing it to link two polymer chains. So the procedure would involve incorporating EGDMA into the monomer mixture before initiating polymerization.

Another possibility is a technique like free radical polymerization, which uses initiators like benzoyl peroxide. But that's more about initiating the polymerization rather than cross-linking. The cross-linking is specifically about adding the cross-linker molecule.

So the correct procedure is the addition of a cross-linking agent like EGDMA. The other options might be incorrect if they mention physical methods like UV light or heat without the cross-linker, or if they refer to other additives that don't induce cross-linking. For example, a plasticizer would make the material more flexible, not cross-linked. Or maybe a different type of initiator that doesn't affect the cross-linking structure.

Therefore, the key point here is the use of a cross-linking agent during polymerization to create the 3D network. The clinical pearl would be that cross-linking agents like EGDMA are essential for the mechanical strength of acrylic prosthetics. The correct answer should be the option that mentions the addition of a cross-linking agent during polymerization.

**Core Concept**
Cross-linking in acrylic polymerization involves forming covalent bonds between linear polymer chains to create a three-dimensional network structure. This process enhances the material's mechanical strength, resistance to deformation, and dimensional stability, critical in applications like dental prosthetics.

**Why the Correct Answer is Right**
The correct procedure involves adding a **cross-linking agent** such as **ethylene glycol dimethacrylate (EGDMA)** during polymerization. This agent has two methacrylate groups that react with linear poly(methyl methacrylate) (PMMA) chains, forming covalent bonds between them. The resulting cross-linked network improves rigidity and durability, making the material suitable for high-stress applications like dentures or bone cements.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect if it refers to a catalyst like benzoyl peroxide

✓ Correct Answer: B. Addition of difunctional monomers