MCQ
“$925$ fine silver” means an alloy of :
- A$7.5 \% \,Ag$ and $92.5\% \ Cu$
- ✓$92.5 \% \, Ag$ and $7.5 \% \, Cu$
- C$80 \% \,Ag$ and $20 \% \, Cu$
- D$90 \% \,Ag$ and $10 \% \,Cu$
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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 $Cu ^{2+}( aq )+ S ^{2-}( aq ) \rightleftharpoons \operatorname{CuS}( s )$ is high because the solubility product is low.
