The least electronegative elements are the?

Hint: The inherent capability for an atom of a particular element to attract shared electrons (or electron density) during the formation of a chemical bond with another atom of the same or different element is known as electronegativity. The electronegativity of an atom is determined by its atomic number as well as the distance between its valence electrons and the charged nucleus.

Complete answer:
Electronegativity is determined by a number of factors which include the nuclear charge and the number and location of other electrons in the atomic shells.
Electronegativity depends on many factors like oxidation state of the element, type of hybridization the element undergoes, type or nature of substituents attached with the atom.
From the definition of electronegativity, we see that higher electronegative elements have the tendency to attract electrons towards themselves. When we move along the period, net increase in effective nuclear charge due to increase in protons and neutrons in the nucleus, due to increase in nuclear strength the size of atoms gradually decreases. Therefore, due to high nuclear charge nucleus shows higher strength of attraction to the outermost electrons to attract them towards itself. Hence, we say that when we move from right to left in a periodic table within the same period electronegativity of an atom increases.
When we move along the group, net decrease in effective nuclear charge is observed due to increase in the size of atoms. Therefore, due to the large size of atoms, nuclear charge shows very less strength of attraction to the outermost shell to attract them towards themselves. Hence, we say that when we move from right to left in a periodic table within the same period electronegativity of an atom increases.
Noble gases are not considered in the periodic table for its general trends because noble gases have full valence shells with complete octet configuration, therefore they refuse to either accept or lose any electrons from it to form a new compound.
From the above discussion we conclude that as we know that noble gases are present at the extreme right of the periodic table and have stable electronic configuration, they tend to show the minimum electronegativity.
 The least electronegative elements are noble gases.
$ \Rightarrow $ The least electronegative elements are noble gases.

Note:
There is Pauling electronegativity scale which is used to determine the strength of electronegativity of atoms. This scale is based on the bond enthalpy of the molecule. Fluorine is considered to be the most electronegative atom with a value of \[4.0\] on the Pauling scale.