What is the net ionic equation for an acid-base reaction between the solution of $Ca{\left( {OH} \right)_2}$ and ${H_2}S$.
A. $C{a^{2 + }} + {S^{2 - }} \to CaS$
B. ${H^ + } + O{H^ - } \to {H_2}O$
C. ${H^ + } + C{a^{2 + }} + {S^{2 - }} + O{H^ - } \to CaS + {H_2}O$
D. $C{a^{2 + }} + {H_2}S + 2O{H^ - } \to CaS + 2{H_2}O$

Hint: Any hydrogen-containing substance capable of donating a proton (hydrogen ion) to another substance is classified as an acid. A base is a molecule or ion that can take a hydrogen ion from an acid and accept it. A chemical reaction between an acid and a base is known as an acid–base reaction. It can be used to figure out what pH is.

Complete answer:
The net ionic equation is a chemical equation that only indicates the elements, compounds, and ions that are directly involved in the reaction. In general, if the molecular equation is correctly calibrated, the net ionic equation would be balanced by both mass and charge.
The equation for acid-base reaction is
$Ca{\left( {OH} \right)_2} + {H_2}S \to CaS + 2{H_2}O$
But in the ionic equation is as follows
$Ca{\left( {OH} \right)_2} \to C{a^{2 + }} + 2O{H^ - }$ ---- (1)
${H_2}S \to 2{H^ + } + {S^{2 - }}$---- (2)
From (1) and (2)
$C{a^{2 + }} + {S^{2 - }} + 2{H^ + } + 2O{H^ - } \to CaS + 2{H_2}O$
Now,
$2{H^ + } + 2O{H^ - } \to 2{H_2}O$
Therefore, the net ionic equation is
$C{a^{2 + }} + {S^{2 - }} \to CaS$
Hence, the correct option is: (A) $C{a^{2 + }} + {S^{2 - }} \to CaS$.

Note:
Both mass and charge must be balanced in net ionic equations. The term "mass balancing" refers to ensuring that the masses of each material on the product and reactant sides are equal. Balancing by charge entails ensuring that the total charge on both sides of the equation is the same. In general, if the molecular equation is correctly calibrated, the net ionic equation would be balanced by both mass and charge.