Which of the following is an illustration of the law of constant composition?

[Wet D]

A. Water boils at 100 degrees Celsius at 1 atm pressure
B. Water is 11% hydrogen and 89% oxygen by mass
C. Water is a compound
D. Water can be separated into other substances by a chemical process
E. Water and salt have different boiling points

 

[steve_geo1]

B. The percents by mass indicate that this is the answer.