Answer:
May be the instrument is incorrect or may be error in it.
Explanation:
The copper have not been detected by this test because the test may be not for the detection of copper, may be it is used for identification of another minerals. If there is copper in the lake sample but can't be detected in the test so it means that the instrument which is used for detection is not the right one or having error in that instrument. Every mineral has a specific type of instrument that detect its presence, if we use incorrect instrument for the mineral then we can't detect the presence of that specific mineral.
The amino acids are the molecules where we can found the carboxyl group (-
), amino group (-
), hydrogen atom (H) and a residual R-group. On the structure of the residual R-group the name of the amino acid depends. Like if R is hydrogen (H) the amino acid is alanine; If R- group is a phenyl group i.e. 
, the compound is called phenyl alanine. The structure of the general amino acid skeleton can be shown as-
I believe it would be the color Red.
