What is the freezing point of a solution of 1.43 g mgcl2 in 100 g of water? kf for water is 1.86°c/m for water.

The answer is b carbon-14. the radioactive isotope of carbon used in carbon dating has a half-life of 5730 years. potassium-40 is used to date 1.25 billion years

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.