Which one of the following elements forms halide in +2 oxidation stat…

The correct answer is Option (4) → Nickel

The highest oxidation state a 3d metal shows in its halides depends on how easily it loses electrons and on the halogen. Fluorine, the most electronegative halogen, brings out the highest states. Along the series the higher oxidation states become less stable, and after the middle of the series the +2 state dominates.

Manganese, iron and cobalt also form halides in higher oxidation states (such as \( \ce{MnF3} \), \( \ce{FeCl3} \) and \( \ce{CoF3} \)), but nickel forms only the +2 halides \( \ce{NiX2} \). So the element that forms halides only in the +2 oxidation state is nickel.

NCERT (2026-27 edition):
Trends in Stability of Higher Oxidation States – “… Table 4.5 shows the stable halides of the 3d series of transition metals. The highest oxidation numbers are achieved in TiX₄ (tetrahalides), VF₅ and CrF₆. The +7 state for Mn is not represented in simple halides but MnO₃F is known, and beyond Mn no metal has a trihalide except FeX₃ and CoF₃.”

Key: X = F → I; X^I = F → Br; X^II = F, Cl; X^III = Cl → I