Everyone loves free stuff, so why not master the magic word in Chinese. It might help you to get a free tea in a Chinese restaurant.

Is it free? -- 是不是免费的 (shì bú shì miǎn fèi de)?

是不是 (shì bú shì ), meaning is it?
是(shì), fourth tone, meaning yes, or is
不是(bú shì ), second tone and fourth tone, meaning is not, or no.

免费(miǎn fèi), third and fourth tone, meaning free.
费 (fèi), fourth tone, means fees
免(miǎn), third tone, means avoid, and is a verb.

You can also just say 免费吗(miǎn fèi ma)?