CBSE Class 9 Answered

Matrix in general is the substance between cells or in which more specialized structures are embedded. So matrix may be intracellular or extracellular. A specific part of the mitochondrion that is the site of oxidation of organic molecules is also called matrix.

Eg of extracellular matrix - Bone cells are embedded in a matrix of collagen fibers and mineral salts. Extracellular matrix is also present in connective tissue.

In the mitochondrion, the matrix contains soluble enzymes  whereas in the cell nucleus, the matrix is the insoluble fraction remaining after extracting the soluble DNA. Golgi apparatus also shows a matrix on its cytoplamsic side.