Which one of the following is considered as a compound?

Calcium carbonate (CaCO3) is a compound because it consists of two or more different elements (calcium, carbon, and oxygen) chemically combined in a fixed ratio. Silicon and Tin are elements, not compounds, as they consist of only one type of atom. Sugar solution is a mixture (homogeneous solution) of sugar and water, not a compound, because its components are not chemically bonded and can be separated by physical means like evaporation. Calcium carbonate, found in limestone, marble, and chalk, has definite chemical properties and a fixed composition (40% Ca, 12% C, 48% O by mass).