A penny is made of the element zinc plated with the element copper; a nickel
is made of a mixture of the elements
nickel and copper. Some isotopes of
various elements are listed below by
their atomic number and mass num-
ber. Use the periodic table on p. 131
to identify which atoms you would
expect to find in the penny, which you
would expect to find in the nickel,
which you would expect to find in
both, and which you would expect to
find in neither coin.​

Asheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200oc and is permitted to achieve a steady-state diffusion condition. the diffusion coefficient for nitrogen in steel at this temperature is 6 x 10- 11 m2 /s, and the diffusion flux is found to be 1.2 x 10-7 kg/m2 -s. also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m3 . how far into the sheet from this high-pressure side will the concentration be 2.0 kg/m3 ? assume a linear concentration profile.