How was it possible that mendeleev was able to predict the properties of elements that no one knew about

Write the complete balanced equation for the reaction between lead (iv) oxide (pbo2) and water (h2o).

Which actions would increase the rate at salt dissolves in water? stir the water? crush the salt? use less water? heat the water? cool the salt

What are the first two quantum numbers for the electrons located in subshell 4d? what are the first three quantum numbers for the electrons located in subshell 2s? how many electrons can be held in a sublevel l = 3? how many electrons can be held in the energy level n = 4? how many electrons in an atom can share the quantum numbers n = 4 and l = 3?