Final answer:
The incorrect statement among the ones provided is that copper liberates hydrogen from acids. Copper does not react with non-oxidizing acids to release hydrogen gas because it is less reactive than hydrogen.
Step-by-step explanation:
The statement that is not correct among the given options is: (i) Copper liberates hydrogen from acids. This is because copper (Cu) is less reactive than hydrogen and does not displace hydrogen from acids. Copper is considered to be below hydrogen in the reactivity series, and therefore does not react with non-oxidizing acids like hydrochloric or sulfuric acid to liberate hydrogen gas. However, it can react with nitric acid, which is an oxidizing acid, through a different reaction mechanism that does not involve the release of hydrogen gas.
Regarding the other statements: (ii) In its higher oxidation states, manganese forms stable compounds with oxygen and fluorine. That's correct since Mn can form MnO2, KMnO4, and MnF3, which are stable. (iii) Mn3+ and Co3+ can act as oxidizing agents in aqueous solution since they have the propensity to gain electrons, going to lower oxidation states Mn2+ and Co2+. (iv) Ti2+ and Cr2+ are indeed reducing agents in aqueous solution because they tend to lose electrons and reach higher oxidation states, such as Ti3+ or Cr3+.