What do cocaine, amphetamines, caffeine, nicotine, and MDMA (ecstasy) all have in common? Select one:

a.
They all increase the activity of the nervous system.

b.
They all cause hallucinations.

c.
They are all taken by people who want to relax or go to sleep.

d.
They are all very highly addictive both physically and psychologically.

A3.37-mg sample of protein was chemically digested to convert its nitrogen into ammonia and then diluted to 100.0 ml. then 10.0 ml of this solution was placed in a 50-ml volumetric flask and treated with 5 ml of phenol solution plus 2 ml of sodium hypochlorite solution. the sample was diluted to 50.0 ml, and the absorbance at 625 nm was measured in a 1.00-cm cuvette and found to be 0.486. for reference, a standard solution was prepared from 10.0 mg of nh4cl (molar mass = 53.49 grams/mole) dissolved in 1.00 l of water. then 10.0 ml of this standard was placed in a 50-ml volumetric flask, treated in the same manner as the unknown, and the absorbance found to be 0.323. finally, a reagent blank was prepared using distilled water in place of unknown, it was treated in the same manner as the unknown, and the absorbance found to be 0.076. calculate the weight percent of nitrogen in the protein.

What term is missing from the central region that describes hypotheses, theories, and laws? popular predictable mathematical falsifiable

The fact that the total amount of energy in a system remains constant is a(n)