Question

Fix the one word that is used incorrectly.
Even
though
the
brain
makes
up
only
two
per
cent
of
you're
total
body
weight
it
uses
up
twenty-five
per
cent
of
the
body's
supply
of
oxygen

Answer 1

Its your not you’re
You’re = your

Answer 2

Even though your brain makes up only two percent of YOUR body.

You’re is a contraction for you are.
Your is a possessive noun for second person.
In this case, it is talking about second persons body, so we will use your.