Which nutrient is not found in the atmosphere (in significant amounts)?

Phosphorous

Explanation:

Phosphorous is an essential nutrient for plants and animals, but is not very common in the biosphere. This nutrient is found in soil and rock, but does not enter the atmosphere.

the last one: artificial selection/genetic engineering

plant breeding is modifying the genetic composition of the plant - but this isn't cloning (which is specifically introducing a gene into a genome). but you are artificially selecting for the phenotype that you want.

the second one is literally genetic engineering - the gene would have been cloned first and then inserted or genetically engineered into the new plant cell (the cotton).