What is meant by valency of elements?

The number of unpaired electrons in the outermost shell of an atom of any element is determined by valency. It provides information on how well one atom may combine with another atom. Therefore, an element's valency describes its capacity to mix with other elements.

The property of an element which give us information about its power of combining with other elements is defined as the valency.

For example- the electronic configuration of oxygen is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^4$. There are $6$ electrons in the outermost shell.

Here p-subshell can accommodate maximum of $6$ electrons and out of $4$ electrons present in p-subshell, $2$ are unpaired.

Multiple valencies are possible for some items. There is no such thing as valency that has a positive or negative sign. The term "valency" derives from the Greek "valentia," which means strength and ability. To comprehend the molecular makeup of both organic and inorganic molecules, this idea was established. Property of an element that gives us information about its power of combining with other elements .

Hence, option 1 is correct.