Given below are two statements: Assertion (A): The total number of geometrical isomers shown by [Co(en)2Cl2]+ complex…
Coordination Compounds · Class 12 · JEE Main Previous Year Question
Given below are two statements: Assertion (A): The total number of geometrical isomers shown by complex ion is three. Reason (R): complex ion has an octahedral geometry. Choose the most appropriate answer:
- a
Both (A) and (R) are correct but (R) is not the correct explanation of (A)
- b✓
(A) is not correct but (R) is correct
- c
Both (A) and (R) are correct and (R) is the correct explanation of (A)
- d
(A) is correct but (R) is not correct
(A) is not correct but (R) is correct
🧠 Geometrical vs Total Stereoisomers
is octahedral.
- Geometrical (cis/trans) isomers: 2 (cis + trans).
- Optical isomers: cis is chiral → 2 enantiomers (Δ-cis, Λ-cis); trans is achiral.
- Total stereoisomers: 2 (cis-Δ, cis-Λ) + 1 trans = 3.
But the assertion says "total number of geometrical isomers is 3". Geometrical isomers = 2 (cis + trans), not 3. The 3 figure includes the optical pair, which are not geometrical.
So A is incorrect.
Reason says " has octahedral geometry" — this is correct.
🗺️ Verdict
A wrong, R correct → option (2).
⚡ Geometrical vs Stereoisomer Vocabulary
| Term | What it counts | |---|---| | Geometrical isomers | cis/trans (and fac/mer) — positional differences | | Optical isomers | Δ/Λ enantiomers — handedness differences | | Stereoisomers | All of the above combined |
The questions often use "geometrical" loosely to mean "stereoisomer" — read carefully.
⚠️ Don't Lump cis-Δ + cis-Λ + trans = 3 "Geometrical"
cis-Δ and cis-Λ have the same geometric arrangement (both cis); they differ only in chirality. So they count as 1 geometrical isomer (cis), not 2.
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