The element lithium has two stable isotopes, lithium $-7$ with an atomic mass of $7\mathrm{.}0160u$ and lithium $-6$ with an atomic mass of $6\mathrm{.}0150u.$ From the atomic mass of $Li=6\mathrm{.}94u$ one can conclude that:

Lithium $-6$ has the highest percent natural abundance

both isotopes have the same percent natural abundance

lithium $-7$ has the highest percent natural abundance