Answer:
a) AlCl3 + 3H2O -> Al(OH)3 + 3HCl
Step-by-step explanation:
A good strategy is to give the most complicated molecule a coefficient of 1 and trace the individual elements to the other side of the reaction. In this case I gave Al(OH)3 a coefficient of 1 which is the same as writing the molecule normally. Then following the first element Al to the other side where its used once in AlCl3, so I gave that a coefficient of 1 because there's only one Al atom in the molecule. Next I focused on the Cl in AlCl3 and looked for other Cl in the reaction, noticing that there is one other instance of Cl present in HCl on the right side of the reaction. I then gave HCl a coefficient of 3 to balance the Cl leaving the final unbalanced molecule H2O, Al(OH)3 contains three H and 3HCl contains another three H making the total H on the right side 6. Since H2O is the only molecule on the left side containing H it's coefficient must be 3.