Which of the following metal ions does not show color in aqueous medium?

$Ti^{4+}$

The correct answer is Option (4) → $Ti^{4+}$

Color in aqueous solutions of transition metal ions arises due to d–d electronic transitions. Ions with no d-electrons (d⁰) or completely filled d-orbitals (d¹⁰) are colorless.

Let’s check each ion:

• Fe³⁺ → $3d^5$ → colored
• Cr³⁺ → $3d^3$ → colored
• V²⁺ → $3d^3$ → colored
• Ti⁴⁺ → $3d^0$ → no d–d transition → colorless