Why it has a valancy of 2?

An element has a valency of 2 when it can form two bonds with other atoms. This typically occurs when the element has two electrons available for bonding in its outer shell, allowing it to either lose or share these electrons. For instance, elements in Group 2 of the Periodic Table, like magnesium and calcium, exhibit a valency of 2 because they have two electrons in their outermost energy level that can be involved in chemical reactions.