Chemistry
Atoms of different elements have

Same number of electrons and neutrons
Different atomic number and same eletronic configu-ration
Same atomic number and same electronic configuration
Different atomic number and different number of valence electrons

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Chemistry
Aqua regia is a 1 : 3 mixture, by volume, of

Conc. sulphuric acid and conc. nitric acid
Conc. nitric acid and conc. sulphuric acid
Conc. hydrochloric acid and conc. nitric acid
Conc. nitric acid and conc. hydrochloric acid

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