The valency of oxygen is:

**The reasoning** Valency is the **combining power** of an element — how many hydrogen atoms (or equivalent) it can bond with. Oxygen has 6 electrons in its outermost shell but *needs* 8 to be stable (the octet rule). So oxygen must gain **2 electrons** to fill up. Look at water: H₂O. One oxygen atom combines with *two* hydrogen atoms. Each hydrogen shares 1 electron, so oxygen shares with 2 hydrogens total. This confirms oxygen's valency = **2**. Same pattern in CO₂, MgO, or any oxide — oxygen always forms 2 bonds. **Why the wrong options tempt you** - **A) 1** — You might confuse valency with the charge in O²⁻ or think of single bonds only. - **C) 3** — Mixing up oxygen with nitrogen (which has valency 3). - **D) 4** — Confusing valency with the atomic number of oxygen's group (Group 6) or carbon's valency. **Quick takeaway** Remember: Oxygen is a "hungry twin" — it always grabs **2 electrons** (or forms 2 bonds) to complete its outer shell, so valency = 2.