Correct option is B
Mobile nutrients in soil are those that can move freely with soil water and are easily available to plants. These include NO₃⁻ (nitrate), Cl⁻ (chloride), and H₃BO₃ (boric acid).
• Cu²⁺ and Fe²⁺ are micronutrients but are relatively immobile.
• NH₄⁺ is less mobile due to adsorption by soil colloids.
Therefore, only option (C) contains exclusively mobile nutrients.