Given below are two statements — Assertion A and Reason R: Assertion A: In TlI3, isomorphous to CsI3, the metal is…
Chemical Bonding · Class 11 · JEE Main Previous Year Question
Given below are two statements — Assertion A and Reason R:
Assertion A: In , isomorphous to , the metal is present in +1 oxidation state.
Reason R: Tl metal has fourteen f electrons in its electronic configuration.
Choose the most appropriate answer:
- a✓
A is correct but R is not correct
- b
Both A and R are correct and R is the correct explanation of A
- c
A is not correct but R is correct
- d
Both A and R are correct but R is NOT the correct explanation of A
A is correct but R is not correct
🧠 is isomorphous with , which is — cesium triiodide, not cesium(III) iodide.
🗺️ Evaluate Assertion A:
: Cs is in +1 state; is the triiodide ion (three iodine atoms, total −1).
Similarly, — Tl is in +1 oxidation state.
This is supported by the inert pair effect: the 6s² electrons of Tl are reluctant to participate in bonding, making +1 the preferred oxidation state over +3.
A is CORRECT ✓
Evaluate Reason R:
Tl (Z = 81):
Tl does have 14 f-electrons (the filled 4f subshell). However, the presence of 14 f-electrons is not the reason Tl prefers +1. The actual reason is the inert pair effect (poor shielding by 4f and 5d electrons increases effective nuclear charge on 6s electrons, making them harder to ionize).
R is NOT the correct explanation of A (and is considered incorrect as a reason)
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