What element has the electron configuration of 1s22s22p63s23p64s23d4?

Chromium (Cr)

Explanation:

To know this, we first need to know, in which group and period of the periodic table is this element. Then, we can identify the element by calculating the atomic number.

In this case, let's write again the electron configuration:

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁴

Now, with the electron configuration we can know the group in which this element is, the period, and the atomic number which will give us the identity of the element.

The period can be identified, by watching the electron configuration and look into the numbers that accompanies the orbitals (The orbitals are the letters s, p and d), and see which one has the highest number. In this case, we have the 4s² , the number 4 is the highest, so the period of this element is period 4.

Now that we know the period, let's determine the group. The group can be determined, watching the electrons of the last cap of the electron configuration (electrons are the numbers superscripted). Now, if the element pass the 3rd period we have to sum the electrons of the previous d cap. In this case, it was. So, we sum 4 electrons of the d orbytal from the previous cap, and the 2 electrons from the 4s, therefore the group of the element is the group 6 (Or column 6 of the table).

Now we know that it's on group 6 and period 4, the final confirmation will be the atomic number of the element. For this, we have to count all the electrons of all capes in the configuration.

Doing this, we have that the sum of all electrons is:

2+2+6+2+6+2+4 = 24

The atomic number of the element is 24.

So to conclude, the element which electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁴, group 6 and period 4, is Chromium (Cr)

the answer is definitely c.