Na-23 has 12 neutrons. What is it’s atomic number?

11

Explanation:

Data obtained from the question include:

Mass number = 23

Neutron = 12

Atomic number =.?

Next, we shall determine the number of protons present in the element.

This can be achieved by doing the following:

Mass number = Proton + Neutron

Mass number = 23

Neutron = 12

Proton =...?

Mass number = Proton + Neutron

23 = Proton + 12

Collect like terms

Proton = 23 – 12

Proton = 11

The atomic number of an element is equal to the proton number.

Atomic number = proton number

Proton number = 11

Atomic number = proton = 11

Therefore, the atomic number is 11.

explanation: no but i do not usually comment

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.