Answer : The value of
for the final reaction is, 
Explanation :
The following equilibrium reactions are :
(1)

(2)

(3)

The final equilibrium reaction is :

Now we have to calculate the value of
for the final reaction.
First half the equation 1, 2 and 3 that means we are taking square root of equilibrium constant and then add all the equation 1, 2 and 3 that means we are multiplying all the equilibrium constant, we get the final equilibrium reaction and the expression of final equilibrium constant is:

Now put all the given values in this expression, we get :


Therefore, the value of
for the final reaction is, 
<h2>Let us complete it :</h2>
Explanation:
let us study about formation of sodium phosphide
Electrons are transferred from atoms of sodium to atoms of phosphorous
The sodium atom looses electrons and the phosphorus atoms
gains electrons .
C. This transfer makes the sodium atoms acquire positive charge and phosphorous acquire negative charge .
As a result, the sodium and phosphorus atoms strongly bond with
each other.
If this is just a general question it seems to vary from about 4.5g to 5g. Is there more data to the question?
My answer to the question is "Gas particles are acting like tiny,solid spheres".
John Dalton
Although the concept of the atom dates back to the ideas of Democritus, the English meteorologist and chemist John Dalton formulated the first modern description of it as the fundamental building block of chemical structures.