For the following Assertion and Reason, the correct option is: Assertion (A): When Cu(II) and sulphide ions are mixed,…
Chemical Equilibrium · Class 11 · JEE Main Previous Year Question
For the following Assertion and Reason, the correct option is:
Assertion (A): When Cu(II) and sulphide ions are mixed, they react together extremely quickly to give a solid.
Reason (R): The equilibrium constant of is high because the solubility product is low.
- a
(A) is false and (R) is true
- b
Both (A) and (R) are false
- c
Both (A) and (R) are true but (R) is NOT the correct explanation of (A)
- d✓
Both (A) and (R) are true and (R) is the correct explanation of (A)
Both (A) and (R) are true and (R) is the correct explanation of (A)
Step 1 — Evaluate Assertion (A): Cu²⁺ and S²⁻ ions react rapidly to form CuS precipitate (extremely insoluble). A is true ✓
Step 2 — Evaluate Reason (R):
- of CuS is extremely small ()
- The equilibrium constant for the precipitation reaction is , which is very large
- A very large means the reaction goes essentially to completion very fast and complete precipitation
- R is true ✓ and correctly explains A
Step 3: The low directly causes the high equilibrium constant for precipitation, which drives the rapid reaction.
Answer: Option (4) — Both true, R is correct explanation
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