Beryllium, magnesium, calcium, strontium, barium, and radium
Elements can combine to form molecules, like o2 or co2. elements combine to form molecules and these elements are joined together by chemical bonds i.e covalent bond in this molecule so option A is correct
hope this helps
The resistance to being scratched is a mineral's hardness
Answer:
dissolving is classified as a physical change because it can be reversed back to its original form
explanation:
Dissolving is an example of a reversible change. For example, when salt is mixed with water it disappears because it dissolves in the water to make salty water. But we can get the salt can back again by boiling off the water. That leaves the salt behind.
Answer:
The solutions should be added in this order NaCl > Na2SO4 > Na2S
Explanation:
Silver is insoluble as a chloride, so the silver ions get precipitated on addition of chloride ion as silver chloride. This means Ag+ would be removed the first.
So we will add NaCl in the first step.
The following reaction will occur.
Ag+ + Cl- → AgCl(s)
Both, Pb2 and Ni are soluble as chlorides. (lead chloride is soluble as a hot solution but will ppt when colder).
When we add Na2SO4, Pb2+ will get precipitated (because it's insoluble) as PbSO4 and Ni will remain soluble as NiSO4 is soluble in water.
The reaction that will occur is:
Pb^2+ + SO4^2- → PbSO4(s)
Nickel is insoluble as a sulfide. So when we will add Na2S, nickel will be precipitated as sulfide and be able to separate and be collected.
The solutions should be added in this order NaCl > Na2SO4 > Na2S