How can an isotope like carbon 14 be used to date dead organisms

  Hello there!
Carbon-14 is a radioactive isotope of carbon that is also organic. It Is in a constant value throughout our lives, and does not decay while within a living organism. Thus it decays just like any radioactive elemental isotopes does. 
So you can use that to date a dead organism based on the carbon 14 because carbon 14 does not Decay.

The correct answer should be "electrons orbit the nucleus in circular motions exactly as shown on the classic bohr model."