Metals usually form cations because they like to lose electrons to get a full octet.
Nonmetals usually form anions because they like to gain electrons to get a full octet.
Aluminum will lose 3 electrons to form a cation
Beryllium will lose 2 electrons to form a cation
Copper can lose either 1 or 2 electrons to form a cation.
Silicon can gain 4 electrons to form an anion.
Your correct answer is silicon.