Final answer:
The correct answer is A) smallest. An atom is the smallest unit of matter that retains the chemical properties of an element, and is the fundamental building block of all matter.
Step-by-step explanation:
The atom is the smallest unit of matter that retains the identity of the substance. This makes answer option A) smallest the correct choice.
An atom is the simplest and smallest particle of matter that still has the chemical properties of the element. Atoms serve as the building blocks for all the elements that constitute matter in both living and non-living entities. Despite their tiny size, with typical dimensions around 100 picometers (1×10−10 m), atoms contain all of the chemical properties of an element. An individual atom of any element, such as gold, retains all the properties characteristic to that element; for example, a gold atom exhibits the same properties as bulk gold, meaning it is a solid metal at room temperature. Atoms are so minuscule that they are only visible with the most powerful microscopes.
Every solid, liquid, gas, and plasma is made up of neutral or ionized atoms. The degree of smallness of atoms is formidable, with approximately fifty million atoms needed to form a line just 1 cm long. Interestingly, the small dot at the end of this sentence would contain several million atoms.