Which of the following compounds is optically active?

• A. $2_{-}$chlorobutane
• B. $1_{-}$propanol
• C. meso-tartaric acid
• D. $n_{-}$butane

Answer: (A)

Verified step by step guidance

1. Identify the presence of chiral centers in each compound. A chiral center is typically a carbon atom bonded to four different groups.
2. For 2-chlorobutane, examine the second carbon to see if it is attached to four distinct substituents, which would make it a stereogenic center.
3. For 1-propanol, check if any carbon has four different groups attached. Since 1-propanol has a primary alcohol group, it usually lacks a chiral center.
4. For meso-tartaric acid, recognize that although it has chiral centers, it is a meso compound, meaning it has an internal plane of symmetry that makes it optically inactive.
5. For n-butane, note that it is a straight-chain alkane with no chiral centers, so it is not optically active.