Now the proton at B is removed and replaced by a lithium nucleus, containing three protons and four neutrons. The proton at location A remains in place. What is the magnitude of the electric force on the lithium nucleus

         F = 3 fo

Explanation:

The electric force is given by Coulomb's law

         F = k q₁ q₂ / r²

where k is the Coulomb constant and is equal to 8.99 109  

with the initial charge the force is  

        Fo = k q₁ q₂ / r²  

        Fo =k q₁ q₂ / r²

In this case it is indicated that charge 1 is changed by the lithium atom a = 3 P  

we substitute  

        F = k 3p p / r²      

        F = 3 (k p² / r²)  

        F = 3 fo

we see that the charge increases by three orders of magnitude

unable to answer the rest since your question is incomplete