Question

The order of filling of electrons in the orbitals of an atom will be

• A. 3d, 4s, 4p 4d, 5s
• B. 4s, 3d, 4p 5s, 4d
• C. 5s, 4p 3d, Ad, 5s
• D. 3d, 4p 4s, Ad, 5s

Answer 1

The Correct Option is B

To determine the order of filling of electrons in the orbitals of an atom, we refer to the "Aufbau principle" which states that electrons fill atomic orbitals in order of increasing energy levels. The approximate order of filling for the first few orbitals is based on the increasing energy levels, and the correct sequence follows the (n+l) rule, where 'n' is the principal quantum number and 'l' is the azimuthal quantum number. The sum of these gives the energy of the orbital. When two orbitals have the same (n+l) value, the orbital with the lower 'n' value fills first.

Let's analyze the given options based on the filling order:

1. Option 1: 3d, 4s, 4p, 4d, 5s
   • Correct order starts with 4s, not 3d as this option incorrectly suggests
2. Option 2: 4s, 3d, 4p, 5s, 4d
   • This matches the expected order as per the Aufbau principle: 4s is filled first then 3d, followed by 4p, 5s, and then 4d
3. Option 3: 5s, 4p, 3d, Ad, 5s
   • Incorrect as it starts with 5s, which should occur after 4p
4. Option 4: 3d, 4p, 4s, Ad, 5s
   • Begins with 3d instead of 4s, and incorrectly places 4s after 4p

After reviewing all the options, the correct order is 4s, 3d, 4p, 5s, 4d, which is provided in Option 2. This is consistent with the filling sequence dictated by the Aufbau principle.