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Solution


Q.

Given below are two statements:

Statement I: The higher oxidation states are more stable down the group among transition elements unlike p-block elements.

Statement II: Copper can not liberate hydrogen from weak acids.

In the light of the above statements, choose the correct answer from the options given below:               [2024]
1 Statement I is true but Statement II is false  
2 Both Statement I and Statement II are true  
3 Statement I is false but Statement II is true  
4 Both Statement I and Statement II are false  

Ans.

(2)

Statement I: In d block elements stability of higher oxidation state increases down the group. For example, in group 6, Mo(VI) and W(VI) are found to be more stable than Cr(VI). Thus Cr(VI) in the form of dichromate in acidic medium is a strong oxidising agent, whereas MoO3 and WO3 are not. In p block elements, stability of lower oxidation state increases down the group due to inert pair effect.

Statement II: ECu2+/Cu∘=+0.34 V,  EH+/H2∘=0 V

For the reaction: Cu+2H+→Cu2++H2

  Ereaction∘=EH+/H2∘-ECu2+/Cu∘=0 V-0.34 V=-0.34 V

Since potential of the reaction is negative copper cannot liberate hydrogen from dilute acids.