Elements and compounds Transitional Reasoning Download PDF

Questions

1. 1.

   In a laboratory investigation, a student examines three pure solid substances labeled X, Y, and Z to determine their classification. Substance X undergoes thermal decomposition at 400 °C to yield a solid residue and a gas with entirely different chemical properties. Substance Y cannot be broken down into simpler substances by any chemical or physical treatment, and spectral analysis confirms it contains only one type of atom. Substance Z maintains a constant composition by mass and is broken down into two distinct elemental gases when subjected to electrolysis. Which statement correctly classifies substances X, Y, and Z based on these experimental results?

   • A) Substances X and Z are homogeneous mixtures because they separate into simpler components upon heating or electrical current.
   • B) Substance Y is a compound because it withstands decomposition under high temperatures, whereas substance Z is an element.
   • C) Substance Y is an element because it consists of only one kind of atom and cannot be chemically broken down, while substances X and Z are compounds.
   • D) Substances X, Y, and Z are all elements because pure substances cannot undergo chemical separation into distinct components.