Answer: option (1) sulfur.
Step-by-step explanation:
1) Brittleness and low conductivity are known properties of solid non-metals.
2) On the contrary, solid metals are known for their ductibility, malleability, and high electrical and thermal conductivity.
3) Sulfur is a non-metal,solid at STP (standard temperature and pressure), so you can expect that it is brittle and a poor conductor.
4) Sodium is a metal, hence it is ductile, malleable and good conductor of electricity and heat.
5) Argon is a non-metal gas at STP, ergo it is not solid.
6) Aluminun is a metal, so it is also ductile, malleable and good conductor.