An electron having quantum numbers $n = 4, l = 3, m = 0, s = -1/2$ is present in which orbital?

Among the elements from atomic number $1$ to $36$,the number of elements which have an unpaired electron in their $s$-subshell is

Following Hund's rule,which element contains six unpaired electrons?

Given below are two statements. One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$ : Energy of $2s$ orbital of hydrogen atom is greater than that of $2s$ orbital of lithium.
Reason $R$ : Energies of the orbitals in the same subshell decrease with increase in the atomic number.
In the light of the above statements,choose the correct answer from the options given below.

Under normal conditions,which of the following electronic configurations is able to form a dipositive ion?

In an atom, the order of increasing energy of electrons with quantum numbers $(i)$ $n=4, l=1$, (ii) $n=4, l=0$, (iii) $n=3, l=2$, and (iv) $n=3, l=1$ is: