The law of conservation of mass states that mass can neither be created nor destroyed. This means that, in a chemical reaction, the mass of reactants should be equal to the mass of products.
The equation we have is:
Al + 3HCl .....> H2 + AlCl3
For aluminum: we have one mole in the reactants and one mole in the products. Therefore, aluminum is balanced
For chlorine: we have three moles in the reactants and three moles in the products. Therefore, chlorine is balanced
For hydrogen: we have three moles in the reactants and only two moles in the products. Therefore, hydrogen needs to be balanced as there are fewer hydrogen moles in the products than in the reactants.
Based on this, the right choice is:
Only hydrogen needs to be balanced. There are equal numbers of aluminum and chlorine.
