Question

Which of the following expressions is a sixth root of unity?

Answer 1

I suspect you know what a root of unity is, right?

Answer 2

any complex number that gives 1 when raised to some integer power n.

Answer 3

You can rewrite 1 in a fancy complex way like this,\[\Large\rm \sqrt[6]{1}=\sqrt[6]{e^{i(0+2k \pi)}}\]and solve for each value that way.
But maybe thinking logically about this one isn't a bad idea instead.