Assertion : Soil particles, particularly clay and organic matter in soil, contain negative charges that attract positively-charged ions such as $\mathrm{Ca}^{++}$, $\mathrm{K}^{+}$and $\mathrm{Mg}^{++}$. Reason : Essential elements derived from soil are termed as mineral elements while those derived from air or water are known as nonmineral elements.

• A

  If both assertion and reason are true and reason is the correct explanation of assertion.
• Correct answer
  B

  Ifboth assertion and reason are true but reason is not the correct explanation of assertion.
• C

  If assertion is true but reason is false.
• D

  If both assertion and reason are false.

Hence, the correct answer is option: 'B'.