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1.Besides gallium, which other elements have since been discovered that were left by Mendeleev in his periodic table ? (any two)
2. In the modern periodic table, which are the metals among the first ten elements ?
Answer variants:
Noble gases are chemically reactive and are present in the atmosphere in extremely low concentrations.
It failed to arrange all the then-known compounds in triads of elements with similar chemical properties.
hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon
Scandium and Germanium.
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