I don't know what the options were but a material that is very likely going to be challenging to recognize under a microscope as a mixture is a homogeneous mixture. A homogenous mixture is uniform and thus hard to recognize as a mixture. An example is water!
The correct chemical formulae is CsBr
Outer ear is the is external part of the ear, consists of the auricle ( also pinna), and the ear canal. It gathers sound energy and focuses it on the ear drum.
