Which elements has two shells, both of which are completely filled with electrons?

Which elements has a total of two shells, with three electrons in its valence shell?

Which elements has a total of three shells, with four electrons in its valence shell?

What is an element? Which of the following are elements?

Which is the last element in the series of the actinoids? Write the electronic configuration of this element. Comment on the possible oxidation state of this element.

The element A has atomic number 15. To which period of the periodic table the element belongs?

Why is copper considered a transition metal, although it has completely filled d-orbital (3d^10) ?

Which element is needed for the synthesis of auxins?

Which element is more reactive - lead or copper?