Answer: Mn 2+.
- A Ti<sup>3+</sup>
- B Mn<sup>2+</sup>
- C Fe<sup>2+</sup>
- D Ni<sup>2+</sup>
Correct answer: B. Mn<sup>2+</sup>
Explanation: Mn<sup>2+</sup> is 3d<sup>5</sup> with 5 unpaired electrons; Ti<sup>3+</sup> (d<sup>1</sup>), Fe<sup>2+</sup> (d<sup>6</sup>, 4 unpaired) and Ni<sup>2+</sup> (d<sup>8</sup>, 2 unpaired) have fewer.
Aqueous solutions of transition metal ions show characteristic colours caused by electrons absorbing visible light to jump between split d-orbitals; the exact colour depends on the metal, its oxidation state, and surrounding ligands.
Concept context
Transition metals (d-block) and lanthanides/actinides (f-block). Known for coloured compounds, variable oxidation states, complex formation, and catalytic properties. Frequently tested in JEE and NEET.