Give two examples of elements with valency 2.

Hint: The valency of the element which expresses the number of bonds that an atom can form in a compound. The element is said to have a complete octet if the outermost shell contains 8 electrons. The atom will complete the outermost shell by gaining, sharing and losing the electrons.

Complete step by step answer: As you know, the valency is the joining capacity of an atom. If valency is two, two types of elements are possible of valency two. One type of element whose outermost shell contains only two electrons. So, they can donate that two electrons and hence their valency becomes two. For example, Magnesium (atomic number = 2) has valency 2, as its electronic configuration is 2, 8, 2. It has two electrons in its outermost shell which is donated to other atoms to complete its octet.
 Another type of element whose outermost shell contains 6 electrons and there is a shortage of two electrons to complete their octet. In that case, this element accepts two electrons from other atoms to complete their octet. For example, Oxygen (atomic number = 8) has valency 2, as its electronic configuration is 2, 6. It accepts two electrons from other atoms to complete its outermost shell.

So, the two examples for the element with valency 2 are Magnesium and Oxygen.

Note: Please note that valency and oxidation number are not the same. Valency is different from the oxidation number, and it has no sign. Thus, the valency of nitrogen is 3, whereas it can have oxidation numbers from -3 to +5. The oxidation number is the hypothetical charge of an atom in a molecule or ion, and it is a measure of its apparent capacity to gain or lose electrons within that species.