Number of neutrons.
The atomic number is a way of identifying elements so if the were all the same than that wouldn't work very well :)
I believe the correct answer from the choices listed above is option D. An object is seen to either speed up, slow down, or change direction due to <span>unbalanced forces. When a system is subjected to unbalanced forces, the object would tend to move or change in motion. Hope this answers the question.</span>
Answer: 
Explanation:
A single displacement reaction is one in which a more reactive element displaces a less reactive element from its salt solution. Thus one element should be different from another element.

Synthesis reaction is defined as the reaction where substances combine in their elemental state to form a single compound.
Decomposition reaction is defined as the reaction where a single substance breaks down into two or more simpler substances.

Combustion is a type of chemical reaction in which hydrocarbons burn in the presence of oxygen to form carbon dioxide and water along with heat.
