Aluminium as Al3+ and Nitride as N3- therefore formula by criss-cross method would be AlN

Chemical Formulas of Compounds:

a) Aluminium Nitride:
Aluminium nitride is a compound composed of aluminium (Al) and nitrogen (N). The chemical formula for aluminium nitride is AlN.

Explanation:
Aluminium nitride is an inorganic compound that belongs to the group III-V compounds. It is a covalently bonded compound formed by the transfer of three electrons from aluminium to nitrogen. Let's break down the formation and the chemical formula of aluminium nitride.

- Aluminium (Al): Aluminium is a metal from Group 13 of the periodic table. It has the atomic number 13 and the atomic symbol Al. In its neutral state, it has three valence electrons.

- Nitrogen (N): Nitrogen is a nonmetal from Group 15 of the periodic table. It has the atomic number 7 and the atomic symbol N. In its neutral state, it has five valence electrons.

- Formation of Aluminium Nitride:
To form aluminium nitride, aluminium transfers three valence electrons to nitrogen. This electron transfer results in the formation of ionic bonds between aluminium and nitrogen atoms.

- Chemical Formula of Aluminium Nitride:
The chemical formula for aluminium nitride can be determined by balancing the charges of the aluminium and nitride ions. Since aluminium loses three electrons and nitrogen gains three electrons, the formula becomes Al3+N3-, which simplifies to AlN.

Therefore, the chemical formula of aluminium nitride is AlN.

b) Ammonium Phosphate:
Ammonium phosphate is a compound containing the ammonium cation (NH4+) and the phosphate anion (PO43-). The chemical formula for ammonium phosphate is (NH4)3PO4.

Explanation:
Ammonium phosphate is an inorganic compound that consists of ammonium ions and phosphate ions. Let's break down the formation and the chemical formula of ammonium phosphate.

- Ammonium (NH4+): Ammonium is a polyatomic cation consisting of one nitrogen atom bonded to four hydrogen atoms. It has a positive charge of +1.

- Phosphate (PO43-): Phosphate is a polyatomic anion consisting of one phosphorus atom bonded to four oxygen atoms. It has a negative charge of -3.

- Formation of Ammonium Phosphate:
To form ammonium phosphate, three ammonium ions (NH4+) combine with one phosphate ion (PO43-). The charges of the ions balance each other, resulting in a neutral compound.

- Chemical Formula of Ammonium Phosphate:
The chemical formula for ammonium phosphate can be determined by balancing the charges of the ammonium and phosphate ions. Since three ammonium ions are required to balance the charge of one phosphate ion, the formula becomes (NH4)3PO4.

Therefore, the chemical formula of ammonium phosphate is (NH4)3PO4.

Aluminium nitride - AlN
Aluminium phosphate - (NH4)PO4...