Answer.
The final solution
Instead of using the word challenging you can use the word gifted, special, special gifted.
Will, when, why, it, can
or
The word you are looking for is "heterogeneous." This term describes a solution where the molecules are not evenly distributed and instead are arranged in different regions or phases within the solution.
Myself
I have a stomach ache.
mixture
are
used to be
is, it, in the past.
no "It" is not used instead of he and she...