Periodic Table And Electron Configuration

1s² 2s¹, 1s² 2s² 2p⁴, 1s² 2s² 2p⁶

Second period elements have their outermost electrons in the second shell (n=2). The 3s¹ configuration belongs to the third period, and 1s² 2p² violates the filling order (2s must be filled before 2p).

5

For d subshell, l = 2. Number of orbitals = 2l + 1 = 2(2) + 1 = 5. Each d subshell contains 5 orbitals, which can accommodate a maximum of 10 electrons.

It decreases down a group, It increases across a period from left to right, s-block elements have relatively low ionization enthalpy

Ionization enthalpy decreases down a group due to increased atomic size and decreases nuclear attraction. It increases across a period due to increased nuclear charge. s-block elements easily lose electrons, so they have low ionization enthalpy.

4

The period number equals the highest shell number (principal quantum number) in the electron configuration. Here, the highest shell is 4 (4s²), so the element belongs to period 4.