Biologists weigh the advantages and disadvantages of survey methods before choosing the appropriate approach. Read through each of the survey methods within the “Where are They” and “How Many” sections and use the table below to organize your thoughts.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds

its temperature is increasing. this causes molecular vibrations to increase.