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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

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e

the answer is d.) potassium