Answer: Water
Explanation: Compound is a substance which is formed by the linkage of different or same kind of atoms.
It is absically composed of two or more elements.
Thus out of the given options, sand is composed of Silica (Si) , gold (Au) is the single element, Iodine (I2) is an diatomic element itself.
Water is made up of 2 moles of hydroge and one mole of oxygen. Thus it will be considered as a compound.