<u>Answer:</u> The element which is most likely to form negative ion is fluorine.
<u>Explanation:</u>
An ion is formed when a neutral atom looses or gains electrons.
- When an atom looses electrons, it results in the formation of positive ion known as cation.
- When an atom gains electrons, it results in the formation of negative ion known as anion.
For the given options:
- <u>Option A:</u> Aluminium
Aluminium is the 13th element of the periodic table having electronic configuration of 
This element will loose 3 electrons to attain stable electronic configuration and will form
ion
Copper is the 29th element of the periodic table having electronic configuration of 
This element will loose 2 electrons to attain stable electronic configuration and will form
ion
Sodium is the 11th element of the periodic table having electronic configuration of 
This element will loose 1 electron to attain stable electronic configuration and will form
ion
- <u>Option D:</u> Fluorine
Fluorine is the 9th element of the periodic table having electronic configuration of 
This element will gain 1 electron to attain stable electronic configuration and will form
ion
Hence, the element which is most likely to form negative ion is fluorine.