Which phenomenon causes exceptions to the electron configuration predicted by the aufbau principle? A. Electrons occupy the lowest energy levels first. B. An atomic orbital may describe at most two electrons. C. The location of an electron at a given time cannot be known exactly. D. Some half-filled energy sublevels are more stable than partially filled sublevels.

c. 75.7

i think that is the right

2b2t

explanation:

2b2t

percent abundance for cu-63 can be shown as:

63 x + 65 (1-x) = 62.9296

65 - 62.9296 = 2 x

x = 1.035

thus, percent abundance for cu-63 is 1.035

percent abundance for cu-65 can be shown as:

63 x + 65 (1-x) = 64.9278

65 - 64.9278 = 2 x

x = 0.0361

thus, percent abundance for cu-63 is 0.0361

the mass spectrum of cu-63 showing the intense peak as, this isotope is found in nature more abundantly around 92.38 % in comparison to cu-65 which is found 62.58 % naturally