Oxidation States of Elements

Let's analyze each statement regarding the oxidation states and compounds of Group 8 elements, Iron (Fe), Manganese (Mn), Technetium (Tc), and Rhenium (Re).

Group 8 Element Oxidation States in Oxides vs Fluorides

Statement (A) says: The highest oxidation state of Group 8 elements is more readily shown in their oxides than in fluorides.

• Group 8 elements include Iron (Fe), Ruthenium (Ru), and Osmium (Os).
• Oxygen is highly electronegative and can stabilize very high oxidation states, especially when multiple oxygen atoms are bonded to a central metal atom. Examples include RuO₄ and OsO₄, where Ru and Os are in the +8 oxidation state.
• Fluorine is the most electronegative element, but its smaller size and ability to form single bonds often limit the coordination number around a central atom compared to oxygen, which can form multiple bonds or exist in species like the oxide ion (O^2-).
• While OsF₈ exists, OsO₄ (+8) is a more common and stable compound demonstrating the highest oxidation state for Osmium. Ruthenium forms RuO₄ (+8) and RuF₆ (+6). Iron typically shows a maximum oxidation state of +6 (e.g., in K₂FeO₄) with oxygen, while its highest common oxidation state with fluorine is +3 (e.g., FeF₃).
• Therefore, for these elements, the highest possible or most readily achieved high oxidation states are indeed often observed in their oxides rather than fluorides.

Statement (A) appears to be correct.

Iron (Fe) Negative Oxidation State

Statement (B) says: Fe can exist in −2 formal oxidation state also.

• Transition metals, including Iron (Fe), can exhibit negative oxidation states, particularly in complexes with ligands like carbon monoxide (CO).
• In such complexes, the metal back-donates electron density into the $\pi^*$ antibonding orbitals of the ligands. This requires the metal to gain electron density initially, leading to a formal negative oxidation state.
• An example is the salt sodium tetracarbonylferrate, Na₂[Fe(CO)₄]. In the anion [Fe(CO)₄]^2-, each CO ligand is neutral. For the overall charge to be -2, the formal oxidation state of Iron must be -2.
• $x + 4(0) = -2 \implies x = -2$.

Statement (B) appears to be correct.

Manganese (Mn), Technetium (Tc), Rhenium (Re) M(II) Compounds

Statement (C) says: Mn, Tc and Re easily form M(II) compounds.

• Manganese (Mn) readily forms stable compounds in the +2 oxidation state, such as MnSO₄ or MnCl₂. Mn²⁺ is a common and stable ion due to its half-filled d⁵ configuration.
• Technetium (Tc) and Rhenium (Re) are heavier congeners in the same group (Group 7, not Group 8 as listed in the question, which seems to contain a typo. Assuming the question meant Group 7 elements Mn, Tc, Re). Let's proceed with the given elements Mn, Tc, Re. These are Group 7 elements.
• Technetium (Tc) and Rhenium (Re) show a strong preference for higher oxidation states, such as +4, +5, and +7 (e.g., TcO₄^-, ReO₄^-).
• While M(II) compounds of Tc and Re exist (e.g., ReCl₂), they are significantly less common and less stable than the M(II) compounds of Manganese. They are not formed "easily" in typical chemical reactions compared to their higher oxidation state counterparts or compared to Mn(II) compounds.
• Therefore, the statement that Mn, Tc, and Re easily form M(II) compounds is only true for Mn; it is not generally true for all three elements.

Statement (C) appears to be incorrect.

Identifying the Correct Statements

Based on the analysis:

• Statement (A) is correct.
• Statement (B) is correct.
• Statement (C) is incorrect.

The correct statement(s) is/are A and B.