Optimum temperature is the temperature at which an enzyme
(a)Work at its best
(b)Is not destroyed
(c)Action is reversed
(d)Is inactivated

Hint: Enzymes are made up of proteins which accelerates the rate of the reaction. It lowers the activation energy and converts the reactants into the substrate. Temperature and pressure are the conditions during this reaction.

Complete answer:
The increased temperature increases the kinetic energy of the enzymes which further accelerates the activity of the enzyme but at a higher temperature, it gets denatured as the peptide bonds between the protein molecules breaks which disrupt the structure of enzymes. It requires an optimum temperature for its activation. High temperature denatures the enzyme and low temperature deactivates the enzyme. Hence it is important to have an optimum temperature for the activation of the enzyme.

Additional Information: -The optimum temp of enzymes is 20-35°C. They become inactivated at very low temperature and denatured (destroyed) at very high temp i.e. greater than 45°C. Low molecular weight enzymes are comparatively more heat stable. In archaebacterium Pyrococcus furiosus, the optimum temperature of hydrogenase is bigger than 95°C. This heat-stable enzyme makes the Pyrococcus grow at 100°C.
-Increases in temperature increase molecular activity and may end at a better rate of collisions between enzymes and substrates. If the temperature rises too high, however, the enzymes could become denatured, and therefore the positive effects of the temperature increase might be nullified.

So, the correct answer is, “Work at its best”.

Note: Enzyme Active Site and Substrate Specificity
Enzymes bind with chemical reactants called substrates. There could also be one or more substrates for every type of enzyme, depending on the type of reaction. In some reactions, a single-reactant substrate is broken into multiple products. In others, two substrates may come together to make one larger molecule. Two reactants may also enter a reaction, both become modified and leave the reaction as two products.
The enzyme’s active site binds to the substrate. Since enzymes are proteins, this site consists of a single combination of amino acid residues (side chains or R groups). Each organic compound residue is often large or small; weakly acidic or basic; hydrophilic or hydrophobic; and positively-charged, negatively-charged, or neutral. The positions, sequences, structures, and properties of those residues create a really specific chemical environment within the site. A specific chemical substrate matches this site like a puzzle piece and makes the enzyme specific to its substrate.