Answer
(a) $^{11}B$
(b) $^{7}Li$
(c) $^{14}N$
(d) $^{20}Ne$
Work Step by Step
To figure out which isotope is more abundant, we don't need to do any calculations. We look at the average atomic mass that is given and see whether this value is closer to the mass number given for each of the isotopes. The isotope with the mass number closest to the average atomic mass of the element is the one with the greatest abundance in nature.
(a) The average atomic mass given for boron (B), 10.81 amu, is closer to $^{11}B$.
(b) The average atomic mass given for lithium (Li), 6.941 amu, is closer to $^{7}Li$.
(c) The average atomic mass given for nitrogen (N), 14.01 amu, is closer to $^{14}N$.
(d) The average atomic mass given for neon (Ne), 20.18 amu, is closer to $^{20}Ne$.
