None of the statements is true of nonmetallic metals.
Nonmetallic metals are not a recognized classification of materials. Metals are elements that have a characteristic luster, are good conductors of heat and electricity, and are generally malleable and ductile. Nonmetals, on the other hand, tend to be brittle, poor conductors of heat and electricity, and have a variety of physical properties.
It is possible that the term "nonmetallic metals" is a confusion or misnomer with the term "metallic minerals", which refers to naturally occurring inorganic compounds that contain metals in their composition. Metallic minerals are often mined for their metal content, and have many uses in industry, construction, and technology. Examples of metallic minerals include copper, iron, gold, silver, and aluminum.
Therefore, option a) is not true because metallic minerals are indeed mined for their metal content. Option b) is not true because nonmetallic metals are not a recognized classification. Option c) is not true because metallic minerals have value. Option d) is not true because nonmetallic metals do not exist.