What is Nutrient X?
Nutrient X is any nutrient that you require, that you are insufficient/deficient in (to understand the differences between the two, read this). Let's say you discovered that you were indeed deficient in chromium (because you experienced symptoms that were diagnosed as a possible lack of sufficient chromium and then you supplemented with chromium and the symptoms resolved), what are the odds that chromium was the only nutrient you were deficient in? Not likely. Based on the way the foods you are eating were grown, it is likely that there are other nutrients your body is not getting enough of to operate at an optimal level.
I have found what I term "problematic" nutrients... the ones that most people seem to be insufficient/deficient in, especially those people not consuming foods fortified with the nutrients that once caused widespread deficiency diseases such as rickets, goiter, and pernicious anemia. Fortunately there are worthwhile tests for most of the problematic nutrients, and easy corrective steps that can be taken (supplementing with "Nutrient X" to bring you back to sufficiency and then to keep you there). But there aren't meaningful tests for all the nutrients your body needs, which is why I recommend a multi-nutrient supplement like Daily Green Boost.
And to those who say that supplements don't work, or that we don't need them, tell that to all the people I've personally helped get rid of minor and major health problems through the prudent use of appropriate amounts of worthwhile nutritional supplementation. I think it's better to deal with reality instead of clinging to disproven, dogmatic rhetoric, especially where your health is concerned.