Hint: Copper does not reduce H⁺ ion from the acid

1. Copper lies below hydrogen in the electrochemical series and hence does not liberate H, from acids. The electrode potential value for Cu is -0.34 V and H⁺ ion is zero. Hence the first statement is incorrect. 

2. In its higher oxidation states, manganese forms stable compounds with oxygen and fluorine. Oxygen and fluorine stabilized the higher oxidation state of manganese. Thus, statement second is correct.

3. Oxidizing agents are those which oxidize other compounds and get reduced themselves.
Mn³⁺ (d⁶) can act as a stronger oxidizing agent because Mn²⁺ is a d⁵ configuration and it is stable. The electrode potential value is as follows:

Mn³⁺/Mn²⁺ = +1.57
Co³⁺/Co²⁺ = +1.97

Hence, it is a correct statement.

4. Ti²⁺ and Cr²⁺ are reducing agents in an aqueous solution. Cr²⁺ is reducing as its configuration changes from d⁴ to d³, the latter having a half-filled t_2g level. Hence, statement is also correct. 









Therefore, option (a) is not correct. The other three options (b, c, d) are correct.