The only mammal naturally capable of true sustain flight is​

Bats

Bats are the only mammals capable of true flight. They belong to the Order Chiroptera, which means "winged hand". Although often mistaken for rodents, they are more closely related to primates. Bats first appeared in the Eocene epoch about 58 million years ago.

the only flying mammal is a Bat

not sure if this is what you'r looking for nnew= nold

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