Which substance was developed by chemists

Silk is made by moth larvae, aspirin is derived from tree bark, nylon was made initially in a laboratory, but aspirin and even synthetic silk can be produced by chemists. Of the three, only nylon has no naturally occur source.

the ratio of the conjugate base to the acid required to attain the desired ph.

c-14 is carbon-14, or radiocarbon.   it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.