Balance the equation Ca0 + HNO3 arrow Ca (N03) 2 + H20

You don't normally do this, but you might start by balancing the complex ion which is NO3^-

There are 2 of these on the right side of the arrow so make two on the left.

CaO + 2HNO3 arrow Ca (NO3) 2 + H2O

That looks balanced. Let's check it out.

Species Ca H NO3 O

Left 1 2 2 1 on the CaO

Right 1 2 2 1 on the H2O

CaO + 2HNO3 - --> Ca (NO3) 2 + H2O