How can something with different atoms be a pure substance and not a mixture

Describe in detail the melting point behavior of the 80: 20 benzoic acid-mandelic acid mixture

Based on the law of conservation of energy, which statement is false? answer- energy is lost when machines dont work right

Which theory was contradicted by experiments with the photoelectric effect? light spreads out after it passes through a small opening. as soon as light strikes metal, electrons will be ejected. visible light, regardless of color, will cause the ejection of electrons when striking metal. the kinetic energy of ejected electrons depends on the frequency of light that strikes the metal.