i. Calcium phosphate [Ca₃(PO₄)₂] :

There are three calcium atoms, two phosphorus atoms and eight oxygen atoms.

Total number of atoms = 2Ca + 2P + 8O

Hence, there are total 12 atoms.

ii. Hydrogen sulphide (H₂S) :

There are two hydrogen atoms and one sulphur atom.

Total number of atoms = 2H + 1S

Hence, there are total 3 atoms.

iii. Magnesium bromide (MgBr₂) :

There are two bromine atoms and one magnesium atom.

Total number of atoms = 2Br + 1Mg

Hence, there are total 3 atoms.

iv. Sodium oxide (Na₂O):

There are two sodium atoms and one oxygen atom.

Total number of atoms = 2Na + 1O

Hence, there are total 3 atoms.

v. Aluminium hydroxide [Al(OH)₃]:

There are three hydrogen and oxygen atoms and one atom of aluminum.

Total number of atoms = 3H + 3O + 1Al

Hence, there are total 7 atoms.