Boojho found a bag containing the following materials

(i) Mirror

(ii) Paper stained with oil

(iii) Magnet

(iv) Glass spectacles

Help Boojho in finding out the material(s) which is/are opaque.

Opaque: Those substances or materials, through which things cannot be seen, are called opaque.

Among the given options, mirror and magnet are the materials through which things cannot be seen. Hence, they both are opaque materials.