Sure! It looks like you're working on balancing chemical equations. Let's go through each of them:

45. **NH₄NO₃ → N₂O + H₂O**

To balance this equation, we need to ensure that the number of each type of atom on the reactant side (left) matches the number on the product side (right).

- Reactants: 1 N₂, 4 H, 3 O
- Products: 2 N, 2 H, 2 O

Balanced equation:
\[ \text{NH}_4\text{NO}_3 \rightarrow \text{N}_2\text{O} + 2\text{H}_2\text{O} \]

46. **HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O**

- Reactants: 1 Ca, 2 OH, 2 NO₃, 2 H
- Products: 1 Ca, 2 NO₃, 2 H, 1 O

Balanced equation:
\[ 2\text{HNO}_3 + \text{Ca(OH)}_2 \rightarrow \text{Ca(NO}_3)_2 + 2\text{H}_2\text{O} \]

47. **SO₂ + O₂ → SO₃**

This is a synthesis reaction where sulfur dioxide and oxygen combine to form sulfur trioxide.
- Reactants: 1 S, 4 O
- Products: 1 S, 3 O

Balanced equation:
\[ 2\text{SO}_2 + \text{O}_2 \rightarrow 2\text{SO}_3 \]

48. **NO + O₂ → NO₂**

- Reactants: 2 N, 2 O (from O₂)
- Products: 2 N, 4 O

Balanced equation:
\[ 2\text{NO} + \text{O}_2 \rightarrow 2\text{NO}_2 \]

50. **Pb(NO₃)₂ → PbO + NO₂ + O₂**

- Reactants: 1 Pb, 2 NO₃
- Products: 1 Pb, 2 N, 6 O

Balanced equation:
\[ 2\text{Pb(NO}_3)_2 \rightarrow 2\text{PbO} + 4\text{NO}_2 + \text{O}_2 \]

These balanced equations respect the law of conservation of mass by ensuring the same number of each type of atom on both sides of the equation.