Because it is passed essentially intact from father to son, y chromosome research has been particularly useful in improving our understanding of

meteorologists would compare a new weather map with one 24 h old to see how fast a front is moving.

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