Explanation:
The Coulomb's law states that the magnitude of each of the electric forces between two point-at-rest charges is directly proportional to the product of the magnitude of both charges and inversely proportional to the square of the distance that separates them:

In this case we have an electron (-e) and a proton (e), so:

In this case, the electric force is negative, therefore, the force is repulsive and its magnitude is:

The answer is mass. I have to comment more than 20 characters.
Answer:
0.776 m far Pinhole should be placed before the viewing screen
Explanation:
For circular aperture of diameter D will have a bright central maximum of diameter, width is given by

where
is wavelength of helium neon laser = 633 nm, D=10.cm, w=0.12 mm
Pinhole should be placed before the viewing screen is

Answer:
Part a)

Part b)
r = 0.166 m
Explanation:
Part a)
As we know that the energy of the Hydride ion is given as

here we have

also we know that

now we have


Part b)
As we know that magnetic force on the charge is centripetal force
so we have

so we have

so we have

