The pair of compounds having metals in their highest oxidation state is: [Fe(CN)6]³⁻ and [Cu(CN)4]²⁻, MnO₂ and CrO₂Cl₂, [FeCl₄]⁻ and Co₂O₃, [NiCl₄]²⁻ and [CoCl₄]²⁻

Oxidation state range-
Fe(26) s²,3d⁶ range: +2 to +6
Cu(29) d¹⁰,4s¹:+1 to +2
Mn(25) d⁵,4s²:+2 to +7
Cr (24) d⁵,4s¹:+1 to +6
Co (27)=3d⁷,4s²:+2 to +5
Ni(28)=3d⁸,4s²:+2 to +4
[Fe(CN)₆]³⁻
x + 6(-1) = -3
x + (-6) = -3
x = +3
[(Cu)(CN)₄]²⁻
x + 4(-1) = -2
x + (-4) = -2
x = +2
Cu and Fe have highest oxidation state in given option.