Question

The element nitrogen has two stable isotopes, nitrogen-14 with a mass of 14.00 amu and nitrogen-15 with a mass of 15.00 amu. From the atomic weight of N = 14.007 one can conclude that:

nitrogen-14 has the highest percent natural abundance
nitrogen-15 has the highest percent natural abundance
both isotopes have the same percent natural abundance
most nitrogen atoms have a mass of 14.007 amu

Answer 1

nitrogen-14 has the highest percent natural abundance.

Answer 2

To answer this you should know that the way the atomic mass is calculated when there are several isotopes is as the weighted average of the atomic masses of the several isotopes.

Given that there are only two isotopes and that their atomic masses are:
nitrogen - 14: 14.00 uma, and
nitrogen - 15: 15.00 uma

The only way that the weigthed average of tha atomis mass of the element is so close to 14 is that the nitrogen-14 is much more abundant than the nigrogen-15.

Answer: first option.