When 20 g of cold water at 20.6 °C is used to cool down a cup of hot water containing 100g of water that is too hot for tea, at 95.7 °C, what is the final temperature of the slightly cooler water when the mixture has reached equilibrium? Cwater=4.186J/g

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.

The answer is probably c. xylem