[Ti(H2O)6]4+ is coloured while [Sc(H2O)6]3+ is colourless. — Coordination Compounds Chemistry Question

💡 Solution & Explanation

Step 1: Ammonia (NH3) is a Lewis base that coordinates to copper ions through the lone pair of electrons on its nitrogen atom. Step 2: In acidic solutions, the high concentration of protons (H^+) causes ammonia to undergo protonation to form the ammonium ion (NH4^+). Step 3: Because NH4^+ lacks a lone pair of electrons, it cannot coordinate to Cu^2+ ions. Therefore, ammonia coordinates with protons instead of forming the complex, which corresponds to option (d).