The product due to racemization is optically inactive because:

two enantiomers in equal proportion are obtained

The correct answer is option 4. Two enantiomers in equal proportion are obtained.

Racemization refers to the process where an optically active compound transforms into a mixture of equal amounts of its two enantiomers.

Enantiomers are non-superimposable mirror images of a chiral molecule. They have identical physical properties except for their interaction with polarized light, where they rotate it in opposite directions with equal magnitudes.

When a racemized mixture is formed, the opposite rotations of the two enantiomers cancel each other out, resulting in no net rotation of polarized light. Therefore, the mixture behaves as optically inactive, even though both enantiomers are present.

The other options are incorrect because:

(1) While the product is indeed optically inactive, this is a consequence of having equal amounts of both enantiomers, not its sole definition.

(2) Inversion of configuration is a common mechanism for racemization, but it's not the only reason for the product being optically inactive.

(3) Obtaining an enantiomer is not the same as racemization. Racemization specifically involves creating a mixture of both enantiomers in equal amounts, while obtaining an enantiomer simply involves isolating one mirror image from the original optically active mixture.

So, remember that the defining characteristic of an optically inactive product due to racemization is the presence of two enantiomers in equal proportions. This equal mixture cancels out their individual rotations, leading to no net rotation of polarized light.