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5. The coefficients are: 2, 7, 2, 4

6. The coefficients are: 1, 4, 1, 2

Explanation:

5. Balancing the equation.

__NO₂ + __H₂ —> __NH₃ + __H₂O

The above equation can be balance as illustrated below:

NO₂ + H₂ —> NH₃ + H₂O

There are 2 atoms of O on the left side and 1 atom on the right side. It can be balance by writing 2 before NO₂ and 4 before H₂O as shown below:

2NO₂ + H₂ —> NH₃ + 4H₂O

There are 2 atoms of N on the left side and 1 atom on the right side. It can be balance by writing 2 before NH₃ as shown below:

2NO₂ + H₂ —> 2NH₃ + 4H₂O

There are 2 atoms of H on the left side and a total of 14 atoms on the right side. It can be balance by writing 7 before H₂ as shown below:

2NO₂ + 7H₂ —> 2NH₃ + 4H₂O

Now the equation is balanced. Thus, the coefficients are: 2, 7, 2, 4

6. Balancing the equation:

__SiO₂ + __HF —> __SiF₄ + __H₂O

The above equation can be balance as illustrated below:

SiO₂ + HF —> SiF₄ + H₂O

There are 4 atoms of F on the right side and 1 atom on the left side. It can be balance by writing 4 before HF as shown below:

SiO₂ + 4HF —> SiF₄ + H₂O

There are 4 atoms of H on the left side and 2 atoms on the right side. It can be balance by writing 2 before H₂O as shown below:

SiO₂ + 4HF —> SiF₄ + 2H₂O

Now the equation is balanced. Thus, the coefficients are: 1, 4, 1, 2