Answer:
Electric field, 
Explanation:
The following values are provided:
Magnitude of charge, 
Force experienced, 
To determine the electric field at the origin, the formula employed is:




Consequently, the electric field at the origin is
. Hence, this provides the sought solution.
Answer: 
Explanation:
The mean free path of an atom can be calculated using the following equation:
(1)
Where:

is referred to as the Universal gas constant
represents the absolute standard temperature
denotes the diameter of helium atoms
symbolizes Avogadro's number
indicates absolute standard pressure
<pFrom this, we can solve for

using
(1), aiming to determine the radius

of the helium atom:
(2)
(3)
(4)
If the radius equals half of that diameter:
(5)
Eventually:
(6)
(7)
Nonetheless, we were tasked with finding this radius in nanometers. Knowing
:
(8)
Ultimately:
Represents the radius of the helium atom in nanometers.