Final answer:
The average atomic mass of lithium from naturally occurring minerals is calculated using the isotopic composition and mass, resulting in approximately 6.94 amu, which corresponds to option A.
Step-by-step explanation:
The average atomic mass of lithium can be calculated using the isotopic mass and abundance. For lithium from naturally occurring minerals with 7.5% 6Li (mass of 6.01512 amu) and 92.5% 7Li (mass of 7.01600 amu), the calculation would be:
(0.075 × 6.01512 amu) + (0.925 × 7.01600 amu) = 0.451134 amu + 6.4898 amu = 6.940934 amu.
Therefore, rounding to two decimal places, the average atomic mass of lithium from this source would be approximately 6.94 amu, which corresponds to option A.