What is the maximum number of electrons which can be accommodated in an atom in which the highest principal quantum number value is $4$?

Write down about the Hund's rule.

In a multi-electron atom,which of the following orbitals described by the three quantum numbers will have the same energy in the absence of magnetic and electric fields?
$1. n = 1, l = 0, m = 0$
$2. n = 2, l = 0, m = 0$
$3. n = 2, l = 1, m = 1$
$4. n = 3, l = 2, m = 0$
$5. n = 3, l = 2, m = 0$

The principal quantum number $(n)$ represents:

If the given four electronic configurations:
$(i)$ $n=4, l=1$
$(ii)$ $n=4, l=0$
$(iii)$ $n=3, l=2$
$(iv)$ $n=3, l=1$
are arranged in order of increasing energy, then the order will be:

Which of the following orbitals are possible: $1p, 2s, 2p, 3f$?