Final answer:
Mendeleev predicted that the gaps in his periodic table represented elements that were yet to be discovered. The discovery of gallium matched his prediction for eka-aluminum, providing support for his periodic table.
Step-by-step explanation:
Mendeleev predicted that the gaps in his periodic table represented elements that were yet to be discovered. He believed that these missing elements would fit chemically into the spaces he left in the table. Mendeleev predicted that the gaps in his periodic table represented elements that were yet to be discovered. The discovery of gallium matched his prediction for eka-aluminum, providing support for his periodic table.
One such example was the prediction of an element with an atomic mass of 68, which he called eka-aluminum. When gallium was discovered, it closely matched the predicted properties of eka-aluminum, providing strong support for Mendeleev's arrangement of elements.