**Core Concept**
Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a genetic disorder that affects red blood cells' (RBCs) ability to protect themselves from oxidative stress. In G6PD deficiency, RBCs are more susceptible to hemolysis (breakdown) when exposed to oxidative stress, such as that generated by free radicals during an infection.

**Why the Correct Answer is Right**
When RBCs undergo hemolysis, they release their intracellular contents into the bloodstream. One of the key enzymes released is lactate dehydrogenase (LDH). LDH is an enzyme found in nearly all living cells, but it is particularly abundant in RBCs. As RBCs are rapidly broken down, LDH levels in the serum will rise initially. However, the question asks which serum level will decrease as soon as intravascular hemolysis begins. The correct answer is related to the enzyme that is consumed during the hemolysis process.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not directly related to the scenario described. The enzyme in question is not typically associated with the hemolytic process in G6PD deficiency.
* **Option B:** This is a plausible option, but the enzyme in question is not the one that is consumed during hemolysis. We need to look for an enzyme that is directly related to the breakdown of RBCs.
* **Option D:** This option is also not directly related to the scenario described. The enzyme in question is not typically associated with the hemolytic process in G6PD deficiency.

**Clinical Pearl / High-Yield Fact**
In G6PD deficiency, the enzyme glucose-6-phosphate dehydrogenase (G6PD) is deficient, leading to an inability to maintain the reduced state of NADP+ and subsequently, an inability to protect RBCs from oxidative stress. This is a classic exam trap - always remember that G6PD deficiency is related to oxidative stress and hemolysis.

**Correct Answer:** C.