Balance equation HNO₃+Ca(OH)₂ → Ca(NO₃)₂+H₂O

The mass is always conserved in a chemical equation. So, all chemical equations must be balanced.

To balance a chemical equation, we need to put the same number of atoms on each side of the arrow.

Coefficients are used to balance a chemical equation.

In the above question, we add 2 as a coefficient of HNO3 and H2O. Because, on the right hand side of the equation there are two Hydrogen atoms present but on the left hand side, three Hydrogen atoms are present. 

Similarly, on the right hand side, two Nitrogen and seven Oxygen atoms are present. But on the right hand side, five Oxygen and one Nitrogen atoms are present.

Finally, we get the balanced equation as 

2HNO₃+Ca(OH)₂ → Ca(NO₃)₂+2H₂O

Hence, the correct option is A .i.e. 2HNO_₃+Ca(OH)_₂ → Ca(NO_₃)_₂+2H_₂O.