Which of the following acts as negative catalyst?

All the above

A negative catalyst, also known as an inhibitor, is a substance that decreases the rate of a chemical reaction. Let's analyze each option:

1. Ethanol in the oxidation of chloroform:
If ethanol is acting as a negative catalyst in the oxidation of chloroform, it would slow down the reaction. Ethanol might not have a direct inhibitory effect on this reaction, so it's less likely to be a negative catalyst in this case.

2. Lead tetraethyl as an antiknock compound:
Lead tetraethyl is used as an antiknock compound in gasoline to prevent knocking in internal combustion engines. It does this by inhibiting the premature detonation of fuel. In this context, lead tetraethyl can be considered a negative catalyst since it inhibits a specific undesired reaction (knocking).

3. Glycerol in the decomposition of H₂O₂:
Glycerol can act as a negative catalyst for the decomposition of hydrogen peroxide (H₂O₂). Glycerol can decompose H₂O₂ slowly, but it doesn't participate directly in the reaction. Instead, it provides a surface for the decomposition to occur, which effectively reduces the overall rate of the decomposition.

Based on the definitions of a negative catalyst and the provided options, the correct answer is:
4. All the above

Both lead tetraethyl (as an antiknock compound) and glycerol (in the decomposition of H₂O₂) can act as negative catalysts in their respective reactions.