49. Which of the following is the smallest unit of water that retains the composition and chemical properties of the compound?
Answer: D
A molecule
A molecule is the smallest unit of water that retains both its composition and chemical properties. In the case of water, each molecule consists of two hydrogen atoms and one oxygen atom, which together form H₂O.
A) A proton
A proton is a subatomic particle found in the nucleus of an atom and does not represent a complete unit of water. It cannot retain the composition or chemical properties of water by itself, as it lacks the necessary combination of atoms.
B) An atom
An atom is the basic unit of matter and, while it is a component of water molecules, it cannot exist as water on its own. A single atom does not encompass the chemical properties or structure of the water compound.
C) An element
An element consists of atoms that are all the same type, such as hydrogen or oxygen. While elements are building blocks of molecules, they do not represent the smallest unit of water itself, as water is a compound formed from multiple elements.
D) A molecule
A molecule is the correct answer because it is the smallest unit of a compound that retains the chemical properties of that compound. In the case of water, the H₂O molecule maintains the characteristics and behavior associated with water.
Conclusion
The molecule is definitively the smallest unit of water that retains its composition and chemical properties, as it is formed by the combination of hydrogen and oxygen atoms. All other options fail to represent this complete structure, as they either refer to smaller components or individual elements that do not define water as a compound.