Answer :
(a) The minimum uncertainty in an electron's velocity is, 
(b) The minimum uncertainty in a helium atom's velocity is, 
Explanation :
According to the Heisenberg's uncertainty principle,
...........(1)
where,
= uncertainty in position
= uncertainty in momentum
h = Planck's constant
And as we know that the momentum is the product of mass and velocity of an object.

or,
.......(2)
Equating 1 and 2, we get:


(a) Given:
m = mass of electron = 
h = Planck's constant = 
= 
conversion used : 
Now put all the given values in the above formula, we get:


The minimum uncertainty in an electron's velocity is, 
(b) Given:
m = mass of helium atom = 
h = Planck's constant = 
= 
conversion used : 
Now put all the given values in the above formula, we get:


The minimum uncertainty in a helium atom's velocity is, 