The answers is
D. The acid creates cracks in the rocks, which
allow air to circulate through the rock,
causing it to weather
To solve this problem we will apply the concepts related to volume, as a function of length and area, as of mass and density. Later we will take the same concept of resistance and resistivity, equal to the length per unit area. Once obtained from the known constants it will be possible to obtain the area by matching the two equations:
Mass of copper wire
Density
Resistively of copper 
Resistance (R) = 0.390\Omega
Volume is defined as,

(1)
We know that,


(2)
Multiplying equation we have




Therefore the length of the wire is 1.68m
Answer:
8.61 min
Explanation:
original mass= 12.65
first half life = 12.65/2 = 6.325
second half life = 6.325/2 = 3.1625
Note : 3.1625 is the closest to the value (3.115) given so we work with it
total time for decay =17.22
therefore two decays = 17.22/2= 8.61