It's a gas

NEON

This element glows bright red in signs and is part of the noble gas group on the periodic table.

The clue "It's a gas" plays on two meanings of "gas." First, it literally refers to neon as a chemical element in gas form—it’s a noble gas used in bright signs. Second, it’s a pun on the slang phrase "it’s a gas," meaning something is fun or entertaining, which fits neon’s flashy, eye-catching glow. The answer is straightforward once you spot the double meaning.