An example of a trace elements is

Step 1: Analyze the question The question asks which option is a trace element. Trace elements (micronutrients) are minerals that organisms need only in very small amounts.

Step 2: Explain the concept Mineral elements needed by living things fall into two groups:

• Macronutrients (major elements): needed in large amounts. Examples: calcium, potassium, magnesium, nitrogen, phosphorus, sulphur, sodium, chlorine.
• Micronutrients (trace elements): needed in very small amounts. Examples: iron, copper, zinc, manganese, iodine, fluorine, cobalt, molybdenum, boron.

Step 3: Check each option

• A. Potassium: a macronutrient, needed for nerve function and for opening and closing stomata. Not a trace element.
• B. Calcium: a macronutrient, needed for bones, teeth and blood clotting. Not a trace element.
• C. Magnesium: a macronutrient, needed to make chlorophyll in plants. Not a trace element.
• D. Copper: needed only in tiny quantities, for enzyme activity and for some respiratory pigments. It is a trace element.

Step 4: Answer The correct option is D. copper.

Tip: Remember the "big" minerals with the phrase "Ca-K-Mg-N-P-S" (calcium, potassium, magnesium, nitrogen, phosphorus, sulphur), which are the macronutrients. Metals like iron, copper, zinc and manganese, along with iodine and fluorine, are the trace elements that appear again and again in WASSCE, JAMB and NECO questions.