A reaction is said to be balanced when the number of atoms (of one type) is the same in both the reactants and the product side of the equation.
In the given reaction, the reactants are KOH and H2SO4. They combine to form products as shown below:
KOH + H2SO4 → K2(SO4) + H2O
Reactants Products
K = 1 K = 2
O = 5 O = 5
H = 3 H = 2
S = 1 S = 1
From the above atoms tally, it is clear that the K, O and H atoms are unbalanced.
In order to balance it, multiply KOH and H2O by 2, The balanced equation is:
2KOH + H2SO4 → K2(SO4) + 2H2O