Balance the equation: ${\mathrm{HNO}}_3+\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\to \mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{H}}_2\mathrm{O}$

A chemical reaction must have an equal quantity of each element on the reactant side and product side in order for it to be balanced. A chemical equation must be balanced in order to guarantee the application of the law of conservation of matter.

The number of components on the left-hand side (lhs) must match the number of elements on the right-hand side in order for a particular response to be balanced (rhs).
Think about the following chemical equation:

${\mathrm{HNO}}_3+\mathrm{Ca}(\mathrm{OH}{)}_2\to \mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{H}}_2\mathrm{O}$

Consider the number of moles of each element on both reactant and product side:
On the LHS (no of moles of each element):
H−3
N−1
Ca−1
O−5
On the RHS (no of moles of each element):
H−2
N−2
Ca−1
O−7

We must balance it since the number of oxygen, hydrogen, and nitrogen moles on the LHS and RHS are not equal.
Let's first create the HNO₃-2 coefficient by balancing the number of nitrogen moles. The equation will then be:

$2{\mathrm{HNO}}_3+\mathrm{Ca}(\mathrm{OH}{)}_2\to \mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{H}}_2\mathrm{O}$

On the LHS (no of moles of each element):
H−4
N−2
Ca−1
O−8
On the RHS (no of moles of each element):
H−2
N−2
Ca−1
O−7
Now let’s balance the number of moles of H on the LHS and RHS.

Make the H₂O−2 coefficient to bring their numbers into balance. The equation will then be:

$2{\mathrm{HNO}}_3+\mathrm{Ca}(\mathrm{OH}{)}_2\to \mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{H}}_2\mathrm{O}$

On the LHS (no of moles of each element):

On the LHS (no of moles of each element):
H−4
N−2
Ca−1
O−8
On the RHS (no of moles of each element):
H−4
N−2
Ca−1
O−8
Now the number of moles of each element on both sides has been equal and we got the balance chemical equation as:

$2{\mathrm{HNO}}_3+\mathrm{Ca}(\mathrm{OH}{)}_2\to \mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{H}}_2\mathrm{O}$

Hence, option B is correct.