Which wave requires a physical medium through which to travel?

All mechanical waves require a physical medium through which to travel.  If there isn't any, then mechanical waves don't travel.

Mechanical waves are the waves where physical particles are doing the waving.  They include sound waves, ocean waves, ripples on a pond, clarinet waves, Slinky waves, guitar-string waves, rope waves, etc.  

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.

this could be newton#'s law of cooling. the cooling curve is exponential