Q.

A pale green crystalline metal salt of (X) dissolves freely in the water. It gives a brown precipitate on the addition of aq. NaOH. The metal salt solution also gives a black precipitate on bubbling H2S in aqueous medium. An aqueous solution of the metal salt decolourises the pink colour of the permanganate solution. The metal in the metal salt solution is:


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a

Al 

b

Pb

c

Cu

d

Fe

answer is A.

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Detailed Solution

Concept- If a salt reacts with aq. NaOH to produce a product, it must be acidic in nature since only then will it be able to react with a base. Copper salts are often blue in colour, while lead salts are white or black in colour, iron salts are greenish in colour, and aluminium salts are white.
Thus, Iron is the metal in the metal salt solution (Fe).
Ferrous sulphate is a pale green crystalline metal salt (FeSO4). When let to stand, it quickly dissolves in water and produces a brown ppt. of basic ferric sulphate  Fe (OH)(SO4).
4FeSO4+ 2H2O+O24 Fe (OH)(SO4)
On bubbling H2S, the metal salt solution likewise produces a black ppt.
Fe2++H2SFeS+2H+
The pink colour of the permanganate solution is decolourised by an aqueous solution of the metal salt, which produced colourless products.
10FeSO4+8H2SO4+2KMnO45Fe2(SO4)3+2MnSO4+K2SO4+8H2O
As a result, the right answer is iron (Fe), option 1, because the metal (X) contained in the solution satisfies all of the prerequisites.
Hence, the correct option is (1).
 
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