The correct answer is option 'D' - brass.

Explanation:
A compound is a substance that is composed of two or more elements chemically combined in a fixed ratio. It is characterized by the presence of a chemical bond between the atoms. Let's analyze each option to determine which one is not a compound:

a) Marble: Marble is a metamorphic rock composed of minerals such as calcite or dolomite. While it is made up of different compounds, it is not considered a compound itself.

b) Washing soda: Washing soda, also known as sodium carbonate (Na2CO3), is a compound that is commonly used in laundry detergents and cleaning products. It is composed of sodium, carbon, and oxygen atoms chemically bonded together.

c) Quick lime: Quick lime, also known as calcium oxide (CaO), is a compound that is obtained by heating limestone. It is composed of calcium and oxygen atoms chemically bonded together.

d) Brass: Brass is an alloy made primarily of copper (Cu) and zinc (Zn). It is not a compound because it does not involve a chemical bond between the copper and zinc atoms. Instead, it is a mixture of these two elements.

In summary, out of the given options, brass is not a compound. It is an alloy. The other options, marble, washing soda, and quick lime, are compounds because they consist of elements chemically bonded together.