1 mole of potassium chlorate on heating thermally decompose and excess of aluminium is burnt.How many moles of aluminium oxide are formed?

2 KClO3 → 2 KCl + 3 O2
4 Al + 3 O2 → 2 Al2O3

(1 mol KClO3) x (3 mol O2 / 2 mol KClO3) x (2 mol Al2O3 / 3 mol O2) = 1 mol Al2O3

2KClO₃(s) → 2KCl(s) + 3O₂(g) ...... [*]
4Al(s) + 3O₂(g) → 2Al₂O₃(s) ...... [#]

In reaction [*] :
Mole ratio KClO₃ : O₂ = 2 : 3 ...... [1]

In reaction [#] :
Mole ratio O₂ : Al₂O₃ = 3 : 2 ...... [2]

Combine [1] and [2] :
Mole ratio KClO₃ : O₂ : Al₂O₃ = 2 : 3 : 2

No. of moles of KClO₃ decomposed = 1 mol
No. of moles of Al₂O₃ formed = (1 mol) × (2/2) = 1 mol