Which of the choices below best explains why the students were able to identify the unknown as lithium chloride? A. The students added energy to the electrons by adding heat to the compounds. The added energy caused the electrons to move up to a higher energy level, going from the ground state to the excited state. When the electrons moved up to higher energy levels, it caused light to be released in the form of photons of various colors. Together, these photons produce a unique color of light for each compound, which allows the students to identify the unknown correctly. B. The students used heat to add energy to the nucleus of the atom. This added heat caused the nucleus to expand and push all of the electrons outwards. When the atom cools down, the electrons can move back inwards towards the nucleus. This rapid movement of electrons back down towards the nucleus releases a different color of light for each element, as all elements have a different-sized nucleus. C. The students used heat to add energy to the electrons in the lithium chloride. The addition of energy caused electrons in the various energy levels to jump to higher energy levels. When the electrons returned to the ground state, the energy they had absorbed was released in the form of photons of light. Substances can be identified by the color of light produced, since all elements produce a very specific color based on how far their electrons fall. D. The students observed the solution before it was put into the flame and realized it was similar in texture and color to the lithium chloride the teacher showed them. When they saw that both lithium chloride and the unknown produced a red flame, they were sure that the unknown must have been lithium chloride as well.