What is the value of electronegativity of oxygen?

The non-metal that does not exhibit a positive oxidation state is

The correct increasing order of the electronegativity is

If the ionization enthalpy and electron gain enthalpy of an element are $275$ and $86 \ kcal \ mol^{-1}$ respectively,then the electronegativity of the element on the Pauling scale is

Which of these has no unit?

Assertion $:$ Electronegativity of $Al$ is greater than $Tl$.
Reason $:$ In a Boron family,down the group regularly size increases.