first --
OFFICIALLY CORRECT ANSWERS ARE CORRECT!
do not question officially correct answers!
far too many students on this forum make the mistake of questioning the correct answers; please note that doing so is a complete waste of your time and effort. i.e., exactly 0% of the time that you spend posting "isn't this official answer wrong?" is productive, and exactly 100% of that time is wasted.
"is this correct?" is never a productive question to ask about one of GMAC's correct answers. the answer is always yes.
"is this wrong?" / "is this X type of error?" is never a productive question to ask about one of GMAC's correct answers. the answer is always no.
instead, the questions you should be asking about correct official answers, if you don't understand them, are:
"why is this correct?"
"how does this work?"
"what understanding am i lacking that i need to understand this choice?"
this is a small, but hugely significant, change to your way of thinking.
you will suddenly find it much easier to understand the format, style, and conventions of the official problems if you retire the idea that they might be wrong.
considering all the answer choices contain "amount of phosphates", we are stuck with this wording. this means you just misinterpreted what type of noun phosphates is, but now you know. :)