Answer 2.04
Step-by-step explanation
Electronegativity decreases down the group and increases across the period in the periodic table.
In the period two of the periodic table,we have the following values for electronegativities with respect to its elements.
Li...........0.98
Be.........1.57
B..........2.04
C.........2.55
N..........3.04
O...........3.44
F...........3.98
Ne........n.a
The value that should be where M is is 2.04