A rock can be broken down into different kinds of substances by physical processes. No chemical reactions are needed to separate different parts of a rock into pure substances. This is because a rock is a
A. compound
B. element
C. mineral
D. mixture

At a certain temperature the rate of this reaction is first order in hi with a rate constant of : 0.0632s2hig=h2g+i2g suppose a vessel contains hi at a concentration of 1.28m . calculate how long it takes for the concentration of hi to decrease to 17.0% of its initial value. you may assume no other reaction is important. round your answer to 2 significant digits.