Wavelength is:
a. the distance between the top or bottom of a wave and the center of the wave.
b. the number of waves in a certain amount of time.
c. the distance between two identical points on a wave.
d. the noise floor acceptable in recording.

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

several tissues working together form an organ, and several organs together make up an organisms.

the group of cell that carries out special jobs are tissue.