How can you tell if a sample of matter is an element?

Which of the following signs of a chemical reaction are observed in the reaction of potassium with water? precipitate formed temperature change smell produced gas produced color change

The diagram below shows a cell placed in a solution. a cell is shown placed inside a beaker. it is labeled cell. the solution inside the beaker is labeled 40% salt solution and the solution inside the cell is labeled 20% salt solution. only water is allowed to move in and out of the cell. what will most likely happen to the cell? it will expand as water moves out of it. it will shrink as water moves out of it. it will expand as water moves into it. it will shrink as water moves into it.

If you chip a tooth, most likely you will go to the dentist to have the missing material filled in. currently the material used to fill in teeth is a polymer that is flexible when put in, yet is hardened to the strength of a tooth after irradiation with blue light at a wavelength of 461 nm. what is the energy in joules for a photon of light at this wavelength?