How many of the following electron configurations are allowed?

1s22s22p7 1s22s22p62d1 [Ne]4s24p4 [Ar]3d64s2 1s22s22p83s23p4

What about this do you not understand. By the way, leave space like this.

1s2 2s2 2p6 3s2 otherwise it makes no sense.

To determine how many of the given electron configurations are allowed, we need to consider the rules and principles of electron configuration.

1. Pauli Exclusion Principle: This states that no two electrons in an atom can have the same set of four quantum numbers. This means that each orbital can hold a maximum of two electrons with opposite spins.

2. Hund's Rule: According to Hund's Rule, when filling orbitals of equal energy (degenerate), electrons will occupy different orbitals with the same spin before pairing up.

Now let's analyze each electron configuration:

1s^2 2s^2 2p^7: This is the electron configuration of a nitrogen atom, which is allowed.

1s^2 2s^2 2p^6 2d^1: This configuration is not allowed. The 2d sublevel is higher in energy than the 2p sublevel, so electrons will fill the 2p sublevel before moving to 2d.

[Ne] 4s^2 4p^4: This is the electron configuration of a selenium atom, which is allowed.

[Ar] 3d^6 4s^2: This configuration is allowed. It corresponds to the electron configuration of a chromium atom.

1s^2 2s^2 2p^8 3s^2 3p^4: This corresponds to a chlorine atom, which is allowed.

From the above analysis, the allowed electron configurations are:

1s^2 2s^2 2p^7
[Ne] 4s^2 4p^4
[Ar] 3d^6 4s^2
1s^2 2s^2 2p^8 3s^2 3p^4

Thus, a total of 4 electron configurations are allowed.