The number of unpaired electrons in $1s^2, 2s^2 2p^4$ is

Which of the following has the maximum number of unpaired electrons? (Atomic number of $Fe = 26$)

Number of unpaired electrons in $Fe^{+3}$ $(Z = 26)$ is

An atom has $35$ nucleons and an atomic number equal to $17$. The number of electrons with $n = 2$ and $m = 0$ in it is:

Identify the correct statements:
a) In an atom,the maximum number of electrons with $n=4$ and $m_s=+\frac{1}{2}$ is $16$.
b) There are $4$ subshells associated with $n=5$.
c) $n=2, l=1, m_l=0$ and $m_s=-\frac{1}{2}$ is a possible set of quantum numbers.
d) The number of radial nodes for $3s$ orbital is $2$.

The five valence electrons of $P^{15}$ are labeled as $A, B, X, Y, Z$ as shown in the figure. If the spin quantum number of $B$ and $Z$ is $+\frac{1}{2}$,identify the group of electrons that share three identical quantum numbers.