Answer:
Silver ions.
Explanation:
The most extensively studied nanomaterials for water purification and treatment mainly includes zero-valent metal nanoparticles, metal oxides nanoparticles, carbon nanotubules and nanocomposites.
Answer 1
The sample will dissolve in more than 1 minute.
Explanation :-
Generally Solubility and rate of solubility of substances increase with the increase in temperature. So lower the temperature less fast will it dissolve in the same amount of water.
Since at 50 C it takes 1 minute to dissolve, at 20 C which is lower temperature it will take more time to dissolve.
Answer 2
Transition metals
Explanation:-
Hardness depends on the extent of metallic bonding for metals. More the number of electrons more the metallic bonding.
Alkali metals with just 1 valence electron have weak metallic bonding. Alkaline earth metals have just 2 valence electrons. Transition elements has more electrons in penultimate shell and valence shell than lanthanides. Transition metals with most metallic bonding are the hardest
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Elements and compounds are purely homogeneous substances and they have a constant composition throughout. Elements and compounds cannot be separated into their respective constituents by physical means. Compounds and mixtures are made up of different elements or different atoms.