The reaction is as follow,
Ca(OH)₂ + Al₂(SO₄)₃ → CaSO₄ + Al(OH)₃
Ca are balance on both sides,
There are 2 Al at left side and one at right so, multiply Al(OH)₃ by 2 to balance,
So,
Ca(OH)₂ + Al₂(SO₄)₃ → CaSO₄ + 2 Al(OH)₃
Now, Ca and Al are balanced, now balance SO₄, which is 3 at left hand side and one at right hand side, so multiply CaSO₄ on right side by 3, so,
Ca(OH)₂ + Al₂(SO₄)₃ → 3 CaSO₄ + 2 Al(OH)₃
Again Ca got imbalance, so multiply Ca(OH)₂ by 3 to balance Ca, So,
3 Ca(OH)₂ + Al₂(SO₄)₃ → 3 CaSO₄ + 2 Al(OH)₃
The Equation is balance now with respect to every element.
Result:
The Ratio is 3 : 1 : 3 : 2, so, Option-G is correct.