This is an incomplete question, here is a complete question.
In the Bohr model of the hydrogen atom, an electron moves in a circular path around a proton. The speed of the electron is approximately
?
Find the force acting on the electron as it revolves in a circular orbit of radius
.
Answer : The force acting on electron is, 
Explanation :
Formula used :

where,
F = force acting on electrons
m = mass of electrons = 
v = speed of electron = 
r = radius of circular orbit = 
Now put all the given values in the above formula, we get:


Thus, the force acting on electron is, 
Because it is a pure substances <span />
Answer:
13.1275%
Explanation:
Molecular formula of ethanol is C2H5OH
Molar mass of ethanol is 46.0684g/mol
Carbon: 24.02g/mol
Hydrogen: 6.05g/mol
Oxygen: 15.99g/mol
Mass percent of hydrogen = 6/46×100 = 13.1275%
Hope this helps, have a great day!
A picture of a no polar covalent bond