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  4. An aqueous solution of a mixture of two inorganic salts, when treated with dilute HCl, gave a precipitate (P) and filtrate (Q). The precipitate (P) was found to dissolve in hot water. The filtrate (Q) remained unchanged, when treated with H 2 S in a dilute mineral acid medium. However, it gave a precipitate (R) with H 2 S in an ammoniacal medium. The precipitate R gave a coloured solution (S), when treated with H 2 O 2 in an aqueous NaOH medium. The precipitate P contains (1) Pb 2+ (2) Hg 22+ (3) Ag + (4) Hg 2+

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Q. An aqueous solution of a mixture of two inorganic salts, when treated with dilute $HCl$, gave a precipitate $(P)$ and filtrate $(Q)$. The precipitate $(P)$ was found to dissolve in hot water. The filtrate $(Q)$ remained unchanged, when treated with $H _{2} S$ in a dilute mineral acid medium. However, it gave a precipitate $(R)$ with $H _{2} S$ in an ammoniacal medium. The precipitate $R$ gave a coloured solution $(S)$, when treated with $H _{2} O _{2}$ in an aqueous $NaOH$ medium.
The precipitate $P$ contains
(1) $Pb ^{2+}$
(2) $Hg _{2}^{2+}$
(3) $Ag ^{+}$
(4) $Hg ^{2+}$

JEE AdvancedJEE Advanced 2013Organic Chemistry – Some Basic Principles and Techniques

Solution:

PLAN $PbCl_2$ is soluble in hot water.
In ammoniacal medium, cations of group III and IV may be precipitated as hydroxide or sulphide and dissolved in $H_2 O_2$ due to oxidation.
Thus, $P$ is $Pb^{2+}.$

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