**Core Concept**
Non-competitive inhibitors bind to a site other than the active site on an enzyme, altering the enzyme's shape and reducing its activity. This type of inhibition does not change the enzyme's affinity for the substrate, but rather decreases the enzyme's maximum velocity (Vmax).

**Why the Correct Answer is Right**
Arsenate (A) is a competitive inhibitor of enzymes involved in glycolysis, such as phosphoglycerate kinase and phosphoglycerate mutase. It competes with phosphate for binding to the active site of these enzymes, thereby reducing their activity. In contrast, arsenate is not a non-competitive inhibitor because it binds to the active site and competes with the substrate for binding.

**Why Each Wrong Option is Incorrect**
**Option B:** Fluoroacetate is a non-competitive inhibitor of the enzyme aconitase in the citric acid cycle. It binds to a site other than the active site and reduces the enzyme's activity.

**Option C:** Arsenate is listed again as an incorrect option, but it was already established that arsenate is a competitive inhibitor.

**Option D:** Disulfiram is a non-competitive inhibitor of aldehyde dehydrogenase, an enzyme involved in the metabolism of alcohol. It binds to a site other than the active site and reduces the enzyme's activity.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that non-competitive inhibitors bind to a site other than the active site on an enzyme, whereas competitive inhibitors bind to the active site and compete with the substrate for binding.

**✓ Correct Answer: A. arsenate**