Compare two electrons with quantum number sets (4, 2, 1, +½) and (4, 1, 1, +½) based on their four quantum numbers.

For the 1st electron, n=4,l=2,m=1,s=+½
the electron is in 4th shell, d subshell, and having a clockwise spin. (4d)
for 2nd elcetron, n=4,l=1,m=1,s=+½
so, elcetron is in 4th shell, p subshell and having a clockwise spin. (4s).
elcetron in 4s subshell has lower energy than 4d subshell. Both have same spin. and are present in same shell

D)can be increased in a closed system

They can measure  the amount of energy gained or lost