1. different gases mix together to form air and no new comound is formed
2. air has variable composition
3. air shows the properties of its constituent substances
Object permanence is the understanding that objects continue to exist even when they cannot be observed (seen, heard, touched, smelled or sensed in any way
The answer is
option D "electron-cloud model." A electron-cloud model includes: includes positive charge, contains electrons, explains the photoelectric effect, suggests the probable location of electrons. It was also invented by Erwin Schrödinger.
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