Neon or Freon

GAS

It’s what fills balloons, fuels stoves, or escapes with a hiss from a soda can.

"Neon or Freon" hints at the answer by naming two well-known examples of gases. The clue relies on the solver recognizing that both words refer to types of gases—neon is a noble gas used in signs, while Freon is a brand name for refrigerants. Since the answer must fit both, the simple, broad term "GAS" is the solution.