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Answer: Protons
The atom in a sample of an element must contain nuclei with the same number of protons. If the protons change in number, then the element will modify as well.
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Answer:
A and C
Explanation:
The term formula unit is use to indicate Simple-Whole Ratios of ions in a compound. KEY WORD! RATIO!
The average speed is calculated using the following formula
Where

T = 298 K [room temperature]
m = mass of each molecule of oxygen
mass of one mole of oxygen molecules = 32 g / mol
mass of one molecule of oxygen will be = 
mass of one molecule of oxygen will be = 
putting values
average speed = 
Average speed = 482.19 m / s
average speed = 1735.8 km / h
so approx = 1700 km/h