Chemist: The molecules of a certain weed–killer are always present in two forms, one the mirror image of the other. O...

shunhe on December 28, 2019

Hi @ielkind,

There can't be an element of randomness as to which molecule works, as we know that one of the molecules work and one doesn't, and we know which is which. Let's start from the beginning: this is a strengthen question, and so we are looking for something that helps the chemist's argument. What is that argument exactly? The chemist concludes that much of the data on the effects of a weed-killer are likely misleading due to the varying concentrations of its two forms of molecules (one of which kills weeds, the other of which does not) depending on local soil conditions. The argument's a bit confusing because there's a leap in it; it's unclear why the data wouldn't be able to account for these differing soil conditions. A helpful boost to the chemist's argument would explain this and address the data.

(B) gives us this explanation and tells us why the data might be misleading. The laboratory studies that gave us the data on the weed-killer's effects were done almost exclusively in soil types where the weed-killer's molecules were equally concentrated and likely to break down; in other words, basically equal proportions. This, however, might not occur in actual soil conditions in the real world, which are likely not usually of that specific soil type.

(D), on the other hand, tells us the opposite and actually weakens the chemist's argument. (D) tells us that the studies of the weed-killer were carried out in soil samples that resembled those of the real world. If that were the case, we'd expect them to not be misleading when compared to the weed-killer's effectiveness in the real world, which weakens the chemist's argument. Hope this helps, and feel free to ask any further questions if you're still confused.