2,3-dimethylbutane has no chiral centers, so it has only 1 stereoisomer.

2-pentene has two geometric isomers: cis-2-pentene and trans-2-pentene.

1,2-dichloropropane has one chiral center, leading to 2 stereoisomers.

The longest chain has 4 carbons, and there are three methyl groups on the second and third carbons.

The longest carbon chain has 5 carbons, and there are two methyl groups on the second and third carbons.

The maximum number of stereoisomers for a compound with n chiral centers is given by 2^n. For 2 chiral centers, it is 2^2 = 4.

(R)-2-butanol and (S)-2-butanol are enantiomers because they are non-superimposable mirror images.

2,3-butanediol has two chiral centers, leading to 4 stereoisomers, while the others have fewer.

2,3-butanediol is a meso compound because it has two chiral centers but is superimposable on its mirror image.