To determine whether blood and iron are substances or mixtures, we need to understand the definitions of these terms.
A substance, in general, refers to any type of matter that has a fixed composition and distinct properties. It can exist in the form of elements or compounds.
A mixture, on the other hand, is a combination of two or more substances that are physically combined, not chemically bonded. Mixtures can be homogeneous (uniform composition throughout) or heterogeneous (non-uniform composition).
Now, let's consider blood. Blood is composed of various components such as red and white blood cells, platelets, plasma, and dissolved substances like proteins, hormones, and nutrients. Since blood contains multiple different components that are not chemically bonded together, it can be classified as a mixture. Specifically, blood is a heterogeneous mixture because its components are not uniformly distributed.
Moving on to iron, it is an element. Elements are pure substances made up of only one type of atom and cannot be further broken down into simpler substances by ordinary chemical processes. In its pure form, iron consists solely of iron atoms, making it a substance.
To recap, blood can be classified as a mixture because it consists of different components that are physically combined but not chemically bonded, while iron is a substance as it is an element made up of only one type of atom.