Which of the following species is not stable?[SiF6]2−[GeCl6]2−[Sn(OH)6]2−[SiCl6]2−

The stability of these species is determined by the octet rule, which states that atoms are most stable when their outermost electron shell is full, typically with eight electrons.

1. [SiF6]2−: Silicon (Si) is in group 14 of the periodic table and can expand its octet to accommodate more than 8 electrons. It forms six bonds with Fluorine (F), each contributing one electron, and the 2− charge indicates there are two extra electrons. This makes a total of 14 electrons around Si, which is acceptable for third period elements and beyond. So, [SiF6]2− is stable.

2. [GeCl6]2−: Germanium (Ge) is also in group 14 of the periodic table and can expand its octet like Si. It forms six bonds with Chlorine (Cl), each contributing one electron, and the 2− charge indicates there are two extra electrons. This makes a total of 14 electrons around Ge, which is acceptable for third period elements and beyond. So, [GeCl6]2− is stable.

3. [Sn(OH)6]2−: Tin (Sn) is in group 14 of the periodic table and can expand its octet. It forms six bonds with Hydroxide (OH), each contributing one electron, and the 2− charge indicates there are two extra electrons. This makes a total of 14 electrons around Sn, which is acceptable for third period elements and beyond. So, [Sn(OH)6]2− is stable.

4. [SiCl6]2−: Silicon (Si) is in group 14 of the periodic table and can expand its octet. It forms six bonds with Chlorine (Cl), each contributing one electron. However, the 2− charge indicates there are two extra electrons, making a total of 14 electrons around Si. This is not acceptable for Si because it is a second period element and cannot accommodate more than 8 electrons in its valence shell. So, [SiCl6]2− is not stable.

Therefore, the species that is not stable is [SiCl6]2−.