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Q.
At $ \text{30}{{\,}^{\text{o}}}\text{C} $ the solubility of $ A{{g}_{2}}C{{O}_{3}}({{K}_{sp}}=8\times {{10}^{-12}}) $ would be greatest in one litre of
$Ag _{2} CO _{3} \rightleftharpoons 2 Ag ^{+} CO _{3}^{2-}$
Due to the common ion effect, the solubility decreases, so the solubility of $Ag _{2} CO _{3}$ would be greatest in $1\, L$ of $0.05 M NH _{3}$ due to the absence of common ion either $Ag ^{+}$or $CO _{3}^{2-}+ Ag ^{+}$ form complex with $NH _{3}$
$A g^{+}+2 N H_{3} \rightleftharpoons\left[A g\left(N H_{3}\right)_{2}\right]^{+}$