Write the structure of $2,3$-dichlorobutane

The compound is: $\mathrm{CH_3-CH(Cl)-CH(Cl)-CH_3}$

Carbon-2 and carbon-3 are both attached to four different groups, so both are chiral centers.

Check for optical isomerism

Since the molecule has two stereogenic centers, it can form stereoisomers:

• $(2R,3R)$
• $(2S,3S)$
• $(2R,3S)$ or $(2S,3R)$

The pair $(2R,3R)$ and $(2S,3S)$ are non-superimposable mirror images, so the compound shows optical isomerism.

Check for diastereomerism

The meso form $(2R,3S)$ is not a mirror image of $(2R,3R)$ or $(2S,3S)$. Therefore, these are diastereomers of each other.

So, $2,3$-dichlorobutane also shows diastereoisomerism.

Check for geometric isomerism

Geometrical isomerism requires restricted rotation, usually due to a double bond or ring system. Here, there is no such restriction.

Hence, geometrical isomerism is not shown.

Check for structural isomerism

Structural isomerism means same molecular formula but different connectivity. The question asks about $2,3$-dichlorobutane itself; its characteristic isomerism here is stereoisomerism, not structural isomerism.

Evaluate options

• A: Diastereo → Yes
• B: Optical → Yes
• C: Geometric → No
• D: Structural → No

Conclusion

$2,3$-dichlorobutane shows both optical and diastereoisomerism. Since this is given as a single-correct MCQ, the stored answer $\mathrm{B}$ is incomplete/incorrect because option $\mathrm{A}$ is also correct.