Hi!
In the given question, "some number to the power of 4" tells us that we are using exponents, because it states "to the power of".
Therefore, your answer is the first option, χ4.
The first option is the only option that uses exponents.
The other options would be said like such:
2.) "A number 4"
3.) "A number multiplied by 4"
4.) "A number added to 4"
For a similar question, see:
https://brainacademy.pro/question/11818830