Number of unpaired electrons in the ground state of beryllium atom is

Which element is represented by the following electronic configuration?

Which of the following set of quantum numbers represents the highest energy of an atom?

What is the meaning of degenerate orbitals?

Using $s$,$p$,$d$,and $f$ notations,describe the orbital with the following quantum numbers:
$(a)$ $n=1$,$l=0$
$(b)$ $n=3$,$l=1$
$(c)$ $n=4$,$l=2$
$(d)$ $n=4$,$l=3$

The quantum number which explains the line spectra observed as doublets in the case of hydrogen and alkali metals,and doublets and triplets in the case of alkaline earth metals is: