A certain radioactive element has a half-life of one hour. If you start with a 1-g sample of the element at noon, how much of this same element will be left at 3:00 PM?
A) 0.5 gram
B) 0.25 gram
C) 0.125 gram
D) 0.0625 gram
Question 2
A sample of iron weighs more after it rusts because ________.
A) it has expanded into a greater volume
B) rust contains twice as many iron atoms
C) of the additional oxygen it contains
D) Wrong. Iron actually weighs less after it rusts