Particles are arranged in a crystal structure in a sample of:

a) H2 (g)

b) Br2 (L)

c) Ar (g)

d) Ag (s)

The answer is number 4. Ag (s) or Solid Silver. Silver in a solid phase has a face centered cubic crystal structure. Among your choices, silver is the only example of particles that are arranged in their crystal structure while the other choices are gases and liquid. Liquid and gases have loose atoms that do not form crystal structures.