When must scientist conduct controlled experiments ?

Awhite powder is added to a solution. the images show observations made before the powder is added, just after the powder has been added, and a little while later. (the liquid in the small beaker is phenol red solution.) what evidence shows that a chemical change has taken place?

Aecosystem is if it can continue to function over long periods of time

Which of the following is a polyatomic ion? a. calcium, ca2+ b. carbide, c4- c. sulfate, so4 d. selenide, se2-