Answer:
6 atm.
Explanation:
Let the mass of both be m
Then moles of He = m/ 4
Moles of Ne = m/ 20
mole fraction of He = Moles of He/ Total moles = m/4/ (m/4 + m/20) = 0.25 m/0.3m = 0.83
Pressure of He = Mole fraction×total pressure = 0.83 × 6 atm = 5 atm
The equation for percent error is
% Error =

Our experimental is 2.85g/cm^3 and the accepted is 2.7g/cm^3
Thus our % Error = 5.555%
lf a heavy point mass is suspended by a weightless, inextensible and perfectly flexible string from a rigid support, then this arrangement is called simple pendulum.
In practice, however, these requirements cannot be fulfilled. So we use a practical pendulum.
A practical pendulum consists of a small metallic solid sphere suspended by a fine silk thread from a rigid support. This is the practical simple pendulum which is nearest to the ideal simple pendulum.
Note :
The metallic sphere is called the bob.
When the bob is displaced slightly to one side from its mean position and released, it oscillates about its mean position in a vertical plane.