Final answer:
The atomic mass of a hydrogen atom with a negative charge and a relative abundance of 99.0% is 1.01 amu, based on the most common hydrogen isotope and the negligible mass of an extra electron.
Step-by-step explanation:
The atomic mass of a hydrogen atom, which has a charge of one and relative abundance of 99.0%, would be closest to the mass of the most common isotope of hydrogen, which is protium (1 proton and no neutrons). This isotope has an atomic mass very close to 1.00 atomic mass unit (amu). The presence of a negative charge indicates an extra electron, which has a negligible mass compared to the proton (approximately 1/1800 of an amu), so it does not significantly alter the atomic mass.
Therefore, the atomic mass of a negatively charged hydrogen atom, based on its abundance and definition of amu, would be approximately 1.01 amu due to the slight difference in mass between the most abundant hydrogen isotope and the unit defined by carbon-12. Answer choice A) 1.01 amu would be the correct option.