Part A Which sentence best states the central idea of paragraphs 21-22 in "Energy Story"?

A. Materials that are insulators and conductors have a high
resistance to electricity.

B. It is more difficult for electricity to pass through insulators than conductors.

C. Insulators and conductors are able to generate a high amount of electricity

D. Electrons move through rubber easier than they move through
metal.

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.