from the point of view of conductive heat loss, which adaptations would be beneficial to animals living in extremely cold climates?

-- 'Ca' (Calcium) is an element.
-- The proton has a positive charge.
-- Nuclear fusion results in the synthesis of atoms of new elements.
-- H₂O (water) is a chemical compound. 
-- Nuclear fission is a decay of the nucleus.
-- The atomic number of an element is the number of protons 
      in each atom of it.
-- I suppose you're using the Greek letter  η  ('eta', not 'nu') 
      to represent the neutron.
-- I suppose you're using ' e ' to represent the electron.