Which of the following best describes a substitutional alloy?
a) Smaller atoms of a second metal occupy interstitial sites between host metal atoms.
b) Alternate layers of two metals are mechanically bonded while each layer retains its own lattice.
c) Atoms of a second element with a comparable atomic radius replace host metal atoms within the lattice.
d) Metal cations are alternately arranged with non-metal anions, the structure held together by ionic bonds.