The maximum contaminant level (MCL) of 2,4-D is 0.07 mg/L in water. Express this MCL in terms of (a) ppm, (b) ppb, c) weight percent, and (d) moles/m3.

Yes it would be a physical change.

12 is probably the typical age for a first kiss but i think its to young.

There is no reason to think the results are biased or not conducted properly but you should not assume the results are correct just because they were done in a laboratory so the answer would be c. it is likely to be reliable because the results support the conclusion presented.