The type of isomerism exhibited by cis and trans isomers is?

Step 1: Analyze the question You are asked what type of isomerism is shown by cis and trans isomers.

Step 2: The concept Isomers are compounds with the same molecular formula but different arrangements of atoms. The main types are:

• Positional isomerism: the same functional group sits at different positions on the carbon chain (e.g., propan-1-ol and propan-2-ol).
• Functional group isomerism: the compounds have different functional groups (e.g., ethanol and methoxymethane).
• Optical isomerism: the compounds have a chiral carbon and rotate plane-polarized light differently.
• Geometrical (cis-trans) isomerism: the compounds differ in the spatial arrangement of groups around a C=C double bond (or a ring), because rotation about the bond is restricted.

Step 3: Apply it Take but-2-ene, CH₃CH=CHCH₃:

• cis-but-2-ene: both CH₃ groups are on the same side of the double bond.
• trans-but-2-ene: the CH₃ groups are on opposite sides of the double bond.

The formula and the order of atoms are the same. Only the spatial arrangement differs, and that is due to the restricted rotation of the C=C bond. This is geometrical isomerism.

Step 4: Answer The correct option is B. geometrical.

Exam tip: "Cis/trans" means "geometry". Remember that geometrical isomerism needs two things: a C=C bond (restricted rotation), and two different groups on each carbon of the double bond. For example, but-1-ene cannot show it, because one carbon of its double bond has two identical hydrogen atoms.