Answer 2.04
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
Answer:

Explanation:
From the given information, since the molecular mass of the ion M+ is not given;
Let's assume M+ = 58.0423
So, by applying the 13th rule;
we will need to divide the mass by 13, after dividing it;
The quotient n = no. of carbon; &
The addition of the quotient (n) with the remainder r = no. of hydrogen.
So;

So;


From the given information; we have oxygen present, so since the mass of oxygen = 16, we put oxygen in the molecular formula by removing
. Also, since the mass is an even number then Nitrogen is 0.
So, we have:

That's a ketone's functional group :)
hydrogen is the lightest element in the periodic table
there's no question on here