Enzymes

When the substrate binds to the enzyme a new, high-energy transition state structure is formed. It is transient and unstable.

The graph plots potential energy (y-axis) against the progress of the reaction (x-axis), so the label B on the y-axis is the potential energy.
The substrate must pass through a high-energy, unstable intermediate structure before forming the product; the peak of the curve, labelled A, is this transition state.
The difference in energy between the substrate and the transition state is the activation energy.
The taller curve is for the reaction without the enzyme, so the larger energy gap, C, is the activation energy without enzyme.
The enzyme lowers the energy barrier; the smaller gap under the lower curve, D, is the activation energy with enzyme.
Hence A – transition state, B – potential energy, C – activation energy without enzyme, D – activation energy with enzyme.

Almost all enzymes are proteins. The exceptions are some nucleic acids that behave like enzymes, called ribozymes (RNA enzymes). No enzyme is a lipid.
So the statement 'most enzymes are proteins but some are lipids' is wrong.
Each enzyme shows its highest activity at a particular optimum pH (true).
Enzymes are generally denatured at high temperatures, but enzymes isolated from thermophilic organisms living in hot vents and sulphur springs are stable and retain their catalytic power even at 80–90 °C (true).
Enzymes are highly specific for their substrates (true).
Hence the wrong statement is that some enzymes are lipids.