Statement I: Nitrogen forms ammonia, and similarly, arsenic forms arsine.
This statement is correct. Arsenic, much like nitrogen, can produce arsine (AsH₃), a compound with chemical properties comparable to ammonia (NH₃).
Statement II: Antimony is incapable of forming antimony pentoxide.
This statement is incorrect. Antimony is capable of forming antimony pentoxide (Sb₂O₅), a recognized compound of antimony in its highest (+5) oxidation state.
Therefore, the correct conclusion is (2) — Statement I is accurate, while Statement II is inaccurate.