In an esterification reaction between acetic acid and ethanol, which isoptopic substitution would be most useful in determining which reactant loses the -oh group

Answer is beryllium.

The electronegativity trend is that it increases from left to right in a period and from bottom to top in a group. This is why fluorine has the highest electronegativity out of all the elements. So since beryllium is at the very top of the group, it has the highest electronegativity