A specific radioactive isotope is presented for our scientific evaluation for possible use of this isotope within the field of radioisotopic medical tracers. At 1 pm, there are 5.6 grams and at 7 pm, there are 3.2 grams. What's the half-life? A) about 3.2 hours
B) about 7.4 hours
c) about 17.1 hours
D) over 24 hours

Which of these would be caused by a chemical change? a) the formation of lava. b) sedimantary rock layering over time. c) metamorphic rock forming from igneous. d) metamorphic rock eroding to form sedimentary rock.

Inside a flashbulb, oxygen surrounds a thin coil of magnesium. when the flashbulb is set off, a chemical reaction takes place in which magnesium combines with oxygen to form magnesium oxide. which of the chemical equations matches the reaction above? a. mg + o2 mgo2 + energy b. 2mg + o mg2o + energy c. 2mg + o2 2mgo + energy d. mg + o mgo + energy

Astudent conducts an experiment to determine how the amount of water given to a plant affects its growth. what is the independent variable for this experiment?