/bar (grad)

\ 23. Of C, B, and D, which occurred first?\ 24. Of the same three above which was deposited last?\ 25. Of

OA,B,C

, and

D

which is youngest?\ Uranium

(U)

is the parent, lead

(Pb)

is the daughter. The half-life is 6 million years. '\ 26. A rock is found that has

50%U

and

50%Pb

. How many half-lives have passed?\ 27. How old is the rock?\ (1)

80^(2)( ris )/(5)

\ citv