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A student puts one big iron nail each in four test tubes containing solutions of zinc sulphate, aluminium sulphate, copper sulphate and iron sulphate. A reddish brown coating was observed only on the surface of iron nail which was put in the solution of 

A. zinc sulphate B. iron sulphate 

C. copper sulphate D. aluminium sulphate

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Iron is more reactive than copper and hence it can displace only copper from its salt. Iron is less reactive as compared to aluminium or zinc so they will not be displaced from their salts. Also iron will not react with its own salt. So the reddish brown coating on surface of nail is of copper deposition which will be observed only in case of iron nail dipped in copper sulphate solution. 

So the correct answer is c.

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