The question is incomplete, here is the complete question:
An atom of helium has a radius of 31. pm and the average orbital speed of the electrons in it is about
. Calculate the least possible uncertainty in a measurement of the speed of an electron in an atom of helium. Write your answer as a percentage of the average speed, and round it to 2 significant digits
<u>Answer:</u> The percentage of average speed is 41 %
<u>Explanation:</u>
We are given:
Radius of helium atom = 31 pm =
(Conversion factor:
)
So, diameter of helium atom = 
The diameter of the atom will be equal to the uncertainty in position.
The equation representing Heisenberg's uncertainty principle follows:

where,
= uncertainty in position = d = 
= uncertainty in momentum = 
m = mass of electron = 
h = Planck's constant = 
Putting values in above equation, we get:

To calculate the percentage of average speed, we use the equation:

We are given:
Average orbital speed = 
Putting values in above equation, we get:

Hence, the percentage of average speed is 41 %