Question

of the following, which sublevel is filled last? answer: a 3d b 4s c 4p d 4d e 5s

Explanation:

Step1: Determine the order of filling sub - levels using the Aufbau principle

According to the Aufbau principle, the order of filling electron sub - levels is based on the \(n + l\) rule. For a given sub - level \(nl\) (where \(n\) is the principal quantum number and \(l\) is the azimuthal quantum number):

• For \(3d\): \(n = 3\), \(l=2\), so \(n + l=3 + 2=5\)
• For \(4s\): \(n = 4\), \(l = 0\), so \(n + l=4+0 = 4\)
• For \(4p\): \(n = 4\), \(l = 1\), so \(n + l=4 + 1=5\)
• For \(4d\): \(n = 4\), \(l = 2\), so \(n + l=4+2 = 6\)
• For \(5s\): \(n = 5\), \(l = 0\), so \(n + l=5+0 = 5\)

When two sub - levels have the same \(n + l\) value (e.g., \(3d\), \(4p\), and \(5s\) all have \(n + l = 5\)), the sub - level with the lower \(n\) value is filled first.

Step2: Compare the \(n + l\) values

Since \(4d\) has the highest \(n + l\) value (\(n + l=6\)) among the given options, it is filled after \(3d\), \(4s\), \(4p\), and \(5s\)

Answer:

D. \(4d\)