Fire extinguishers are commonly colored red, which aligns with the red of fire trucks and the general association of red with emergencies. Although there is no official standard, altering the colors could lead to confusion, potentially endangering lives. Therefore, it seems that red will likely remain the color of fire extinguishers for the foreseeable future.
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Result:
, 
Explanation:
The electromagnetic attraction between the electron and the proton in the nucleus is equivalent to the centripetal force:

where
k represents the Coulomb constant
e denotes the charge of the electron
e denotes the charge of the proton in the nucleus
r signifies the distance from the electron to the nucleus
v indicates the velocity of the electron
is the mass of the electron
Rearranging for v, we determine

Inside a hydrogen atom, the distance separating the electron from the nucleus is roughly

while the mass of the electron is

and the charge is

By plugging in the values into the formula, we achieve
