Question

which of the following is the correct order of filling the orbitals?
a 1s,2s,2p,2d
b 1s,2s,3s,3p
c 1s,2s,2p,3s
d 1s,2s,2p,2f

Explanation:

According to the Aufbau principle, electrons fill orbitals in order of increasing energy. The energy order of orbitals is \(1s<2s < 2p<3s<3p<4s<3d\cdots\).

• Option a: There is no \(2d\) orbital. The second energy level (\(n = 2\)) has \(s\) (\(l=0\)) and \(p\) (\(l = 1\)) orbitals (\(l\) values range from \(0\) to \(n - 1\), so for \(n=2\), \(l=0,1\)).
• Option b: After \(2s\) and \(2p\) (not \(3s\) immediately after \(2s\)), the order is incorrect as per the Aufbau principle.
• Option c: \(1s\) is filled first (\(n = 1\), \(l=0\)), then \(2s\) (\(n=2\), \(l = 0\)), then \(2p\) (\(n=2\), \(l=1\)), and then \(3s\) (\(n=3\), \(l=0\)) which follows the Aufbau principle.
• Option d: There is no \(2f\) orbital. For \(n = 2\), \(l\) can be \(0\) and \(1\) (no \(l=3\) which is required for \(f\) orbitals (\(l = 3\) for \(f\) orbitals and \(n\geq4\) for \(f\) orbitals to exist as \(l\) ranges from \(0\) to \(n - 1\))).

Answer:

C. \(1s,2s,2p,3s\)