Which of these substances has a regular lattice of positive metal ions in a sea of delocalised electrons?SiO2(s)NaCl(s)O2(g)Na(s)

The substance that has a regular lattice of positive metal ions in a sea of delocalised electrons is Na(s). This is a characteristic of metallic bonding, which is found in pure metals such as sodium (Na).

Here's a step-by-step explanation:

1. SiO2(s) is silicon dioxide, a covalent network solid. In this substance, each silicon atom is bonded to four oxygen atoms and each oxygen atom is bonded to two silicon atoms. This forms a three-dimensional network of strong covalent bonds, not a sea of delocalised electrons.

2. NaCl(s) is sodium chloride, an ionic compound. In this substance, sodium ions (Na+) and chloride ions (Cl-) form a regular lattice structure. However, the electrons are not delocalised; they are transferred from sodium to chlorine in the formation of the compound.

3. O2(g) is oxygen gas, a covalent molecular substance. In this substance, two oxygen atoms share a pair of electrons to form a covalent bond. The electrons are localised between the two oxygen atoms, not delocalised.

4. Na(s) is sodium metal. In this substance, the sodium atoms form a regular lattice and each atom contributes its outer electron to form a 'sea' of delocalised electrons that surrounds the positive metal ions. This is characteristic of metallic bonding.