The correct answer is D. Fluorine.
Oxyacids are compounds that contain oxygen and hydrogen, and are formed when an element reacts with oxygen. The element must have a high enough electronegativity to attract the oxygen atoms, and must also be able to form multiple bonds with oxygen. Fluorine has the highest electronegativity of any element, but it cannot form multiple bonds with oxygen. This is because fluorine has a very small atomic radius, which means that its electrons are held very tightly. As a result, it is difficult for fluorine to share its electrons with oxygen.
Sulphur, chlorine, and nitrogen can all form oxyacids. Sulphur can form sulphuric acid (H2SO4), chloric acid (HClO3), and nitric acid (HNO3). Nitrogen can form nitric acid (HNO3), nitrous acid (HNO2), and nitric oxide (NO).
Oxyacids are important because they are used in many different industries. For example, sulphuric acid is used in the production of fertilizers, chlorine is used in the production of bleach, and nitric acid is used in the production of explosives.