The ion most likely to be leached from the soil is the chloride ion (Cl⁻).

Why chloride (and similar anions) get leached

  • Most soil particles (especially clays and organic matter) carry a negative charge, so they attract and hold cations like K⁺, Ca²⁺, Mg²⁺, and Fe²⁺/Fe³⁺ more strongly.
  • Negatively charged ions (anions) such as chloride (Cl⁻) and nitrate (NO₃⁻) are repelled by these negatively charged particles, so they stay dissolved in the soil water and move freely with percolating rainwater.
  • Because of this, anions like chloride are easily washed down the soil profile and out of the root zone during heavy rains, i.e., they are readily leached.

So, if the options are something like:

  • chlorine (chloride) ions
  • potassium ions
  • iron ions
  • calcium ions

then chloride ions are the ones most likely to be leached from the soil.

Information gathered from public forums or data available on the internet and portrayed here.