Why is it hard to observe winter insects

As the Earth warms overall, insects are shifting toward the poles to colonize areas that are warmer than before in the summer months. Yet many of these insects lack the ability to survive the colder winters found in these regions. ... As the days stay warmer later into the fall, insects' bodies get confused.

Explanation:

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