Which one is larger one ounce or one gram?

That's not a simple question, first of all because "ounce" is a force, not a mass.

On Earth, one ounce is the weight of about 28.3 grams of mass.

On Jupiter, though, it only takes 10.7 grams to weigh one ounce.

And on the sun, one gram of mass would weigh 0.984 ounce ... pretty close to equal.