Question

how many 5s electrons does cr²⁺ have?

Explanation:

Step1: Find atomic number of Cr

From the table, Cr (chromium) has atomic number 24. A neutral Cr atom has 24 electrons.

Step2: Write neutral Cr electron config

Cr is an exception; its ground state electron configuration is $1s^22s^22p^63s^23p^63d^54s^1$ (instead of $3d^44s^2$ for stability).

Step3: Determine $Cr^{2+}$ electron config

When forming $Cr^{2+}$, Cr loses 2 electrons, first from the 4s orbital, then a 3d orbital. So $Cr^{2+}$ has configuration $1s^22s^22p^63s^23p^63d^4$.

Step4: Count 5s electrons

The $Cr^{2+}$ configuration has no electrons in the 5s orbital.

Answer:

0