If a sample of C-14 initially contains 1.2 mmol of C-14, how many millimoles will be left after 2285 years?

The amount of millimoles left after 2285 years is 0.910 millimoles

Explanation:

The half life of  a substance is the time require for a radioactive decaying substance to have decayed int half of its initial quantity. Half life is used to different types or forms of decay such as in nuclear physics, to describe the time of decay of unstable atoms and in medicine to define a drugs half-life

To  solve this, we are required to state the hlf life of C-14 which is 5,730 years

Hence the formula for calculating half life is  

∴ = 0.910 millimoles will be left after 2285 years

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8