The micronutrient needed in smallest amount

The micronutrient needed in the smallest amount by the plant is Molybdenum.
Molybdenum is an essential component in two enzymes that convert nitrate into nitrite and then into ammonia before it is used to synthesize amino acids within the plant. It is also required by symbiotic nitrogen fixing bacteria in legumes to fix atmospheric nitrogen.
The normal range for most plant tissue is between 0.3 - 1.5 ppm.