Stereoisomers

Step 1: Analyze the compounds.
Enantiomers are non-superimposable mirror images of each other. Based on the structure, these two compounds are enantiomers.
Thus, the correct answer is (1).

Step 1: Understand chirality.
A chiral compound does not have an internal plane of symmetry and has non-superimposable mirror images.
Step 2: Conclusion.
Only structures I and II are chiral compounds. Final Answer:

Step 1: Partial hydrogenation of alkyne with Pt gives cis-alkene.
Step 2: Addition of D₂ across double bond occurs syn, forming meso compound.

Step 1: Structure II contains a chiral nitrogen with restricted inversion.
Step 2: This leads to two non-superimposable stereoisomers.

Structures A and B are non-superimposable mirror images, hence they are enantiomers.

Step 1: Presence of a plane of symmetry makes a molecule achiral.
Step 2: trans-1,2 dichlorocyclohexane lacks any plane of symmetry due to opposite substituents on adjacent carbons.
Step 3: Other given structures possess at least one symmetry plane.

Step 1: Partial hydrogenation of 2-butyne with H₂/Pt gives cis-2-butene (syn addition).
Step 2: Addition of D₂ across the double bond also occurs via syn addition.
Step 3: Syn addition on a cis-alkene produces a meso compound.

Step 1: A molecule shows stereoisomerism if it has a chiral center or restricted rotation leading to non-superimposable mirror images.
Step 2: Structure (I) has a tetrahedral nitrogen attached to four different groups, hence it shows optical isomerism.
Step 3: Structure (II) has two identical substituents on nitrogen, so it is achiral.
Step 4: Structure (III) again has four different substituents around nitrogen, making it chiral.

Step 1: Plane of symmetry divides a molecule into two identical halves. Step 2: \beginitemize • trans-1,2 and trans-1,3 substituted cyclohexanes possess symmetry. • cis-1,2-dichloro cyclohexane has no plane of symmetry due to asymmetric axial–equatorial arrangement. \enditemize Step 3: Hence, cis-1,2-dichloro cyclohexane does not contain plane symmetry.