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The element with the highest ionisation potential from the elements of period 1, 2 and 3 is:
A. Li
B. He
C. F
D. Ne

Answer Verified Verified
Hint: The ionisation potential of an element is the amount of the energy which is required to remove the outermost electron from the valence shell. Ionisation energy depends on the atomic size of the atom.

Complete step by step answer:
- In the given question, we identify the element which has the highest value of ionisation potential.
- As we know that to break a bond we need energy so, the ionisation potential or ionisation energy is the amount of energy which is required to remove the electron from the outermost shell by breaking the bond or attraction of the electron with the nucleus.
- As we know that the atomic size increases as we move down the group due to the addition of a new shell due to which the attraction between the nucleus and electron decreases and it becomes easy to remove the electron.
- So, down the group ionisation potential decreases and from left to right along with the period ionisation potential increases.
- So, we can say that the inert gas elements have the highest value of ionisation potential because they are present at the last of each period.
- As we know that helium is a noble gas so it will have the highest value of ionisation potential. Also due to their smaller size than the other element the attraction between nucleus and electron is more.
So, the correct answer is “Option B”.

Note: The second ionisation energy is the energy that is required to remove the second electron from the outermost shell. Similarly third ionisation potential is the energy required to remove the third valence electron and we can also determine successive ionisation potential.
Neon is also a noble gas but it is below helium in the periodic table. So, it has a lower value of ionization potential compared to helium, that's why it is not the correct answer. Don’t confuse among them.
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