The isotope lead-208 (208pb): g/mol the isotope strontium-87 (87sr): g/mol

208 g/mol and 87 g/mol

Explanation: We are given the units as 'g/mol' which are the units of atomic mass.

Atomic mass is the sum of number of protons and number of neutrons.

Atomic number = Number of protons + Number of neutrons

For

Number of neutrons = 126

Number of protons = 82

Atomic mass = 126 + 82 = 208 g/mol

For

Number of neutrons = 49

Number of protons = 38

Atomic Mass = 49 + 38 = 87 g/mol