To develop this problem it is necessary to apply the concepts related to the proportion of a neutron star referring to the sun and density as a function of mass and volume.
Mathematically it can be expressed as

Where
m = Mass (Neutron at this case)
V = Volume
The mass of the neutron star is 1.4times to that of the mass of the sun
The volume of a sphere is determined by the equation
Replacing at the equation we have that



Therefore the density of a neutron star is 
Answer:
1. E=5320.3J
2. E= 1773.45J
3. E=6.76*10^{-21}J
4. E=2.25*10^{-21}J
Explanation:
1. the thermal energy is given by the formula

where KB is the Boltzmann's constant, T is the temperature and N is the number of molecules in the system.
2. Each degree of freedom contains one half of the total energy. Hence, the energy for one degree of freedom is

3.

4.

Hope this helps!!
1(km)cubed = (1,000 m) x (1,000 m) x (1,000 m) = 1 billion cubic meters
1.4 x 10 to the 9 cubic km = 1.4 x 10 to the 9 x (10 to the 9 cubic meters) =
1.4 x 10 to the 18 cubic meters.
There is 1 Mg and 2 Cl i think