The soup.
A can of soup is mostly water, which is pretty dense. A box of cereal is mostly air (I'm thinking rice crispies or corn pops), which is far less dense than water.
But what you should do to...
It depends on how you are using it in a sentence. For instance, I have so many soups in my cabinet. Or if you said I don't like this soup. plural and singular.
Daniel Blake in 1902, he was having toast when he wanted a quciker way to eat breakfast, he ran out to his corn field, and picked some, then ate it whole. Now he is fat.
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