Which element has a crystalline lattice through which electrons flow freely

Copper

Explanation:

Metals are often arranged in crystalline lattices. The lattice consists of metal ions with an overlying sea of electrons. The conductivity of a metal depends on the nature of this crystal lattice. Naturally, some metals conduct electricity better than others. The unique properties of the crystal lattice of copper allow electrons to flow through it freely especially when it is drawn into a wire.

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.