- See charge on ion is -1 .
Hence it has taken 1 electron
Now first look at EC of Fluorine(F)

- Now one electron added .hence no of electrons is 10now
Look at the EC

Or
![\\ \bull\sf\dashrightarrow [He]](https://tex.z-dn.net/?f=%5C%5C%20%5Cbull%5Csf%5Cdashrightarrow%20%5BHe%5D)
Option C is correct.
Answer:
The amount of electric power produced for each unit of thermal power gives the plant its thermal efficiency, and due to the second law of thermodynamics there is an upper limit to how efficient these plants can be.