The number that never changes is the atomic mass (atomic number on the periodic table)
Answer:

Explanation:
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In this case, when balancing chemical reactions, we must make sure that the atoms of each element are the same at both reactants and products; thus, for the given reaction, we need two iron and aluminum atoms at each side based on their subscripts in the given oxides as shown below:

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When you encounter a storm drain, gravel surface or pothole.
Answer:
The process of dissolving can be endothermic (temperature goes down) or exothermic (temperature goes up).
When water dissolves a substance, the water molecules attract and “bond” to the particles (molecules or ions) of the substance causing the particles to separate from each other.
The “bond” that a water molecule makes is not a covalent or ionic bond. It is a strong attraction caused by water’s polarity.
It takes energy to break the bonds between the molecules or ions of the solute.
Energy is released when water molecules bond to the solute molecules or ions.
If it takes more energy to separate the particles of the solute than is released when the water molecules bond to the particles, then the temperature goes down (endothermic).
If it takes less energy to separate the particles of the solute than is released when the water molecules bond to the particles, then the temperature goes up (exothermic).
Explanation:
Answer : Neutrons.
Explanation : Usually in nuclear fission reactions the atoms with a heavy nucleus is bombarded with neutrons. Which breaks the parent atom into many smaller atoms resulting in fission products.