1. what is the difference between an open system, a closed system, and an isolated system? what can a chemist do to try to make a system as isolated as possible?

An open system is a material system in which mass or energy can be lost or gained from the environment, where a closed system is a physical system that doesn't change any matter with its systems. An isolated system is either a physical or a thermodynamic system, in physical science from what i could gather. 

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.

Answer:

a. energy is absorbed in the reaction.

explanation:

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.