Shauna was measuring a radioactive substance in the laboratory. She measured 5.0 kg of substance X at noon Tuesday. At noon Thursday, two days later, Shauna measured 1.25 kg of substance X. What is the half-life of substance X? Explain your answer.

You are making a solution of calcium chloride dissolved in water. you add solid, stir, and it dissolves. you add just a spatula tip full, stir, and the solid does not dissolve. how could you describe the solutions before and after adding the spatula tip amount

Which of these is not an example of chemical weathering? a. iron-rich mineral rusting b. feldspar turning into clay c. limestone reacting with acid d. granite breaking up into sand

The excretory system,need answers for all: )