The atomic number of the element having the maximum number of unpaired electrons (in the ground state) is ........

The electronic configuration $1s^2 2s^2 2p_x^1 2p_y^1 2p_z^1$ corresponds to which of the following elements?

Identify which of the following sets of quantum numbers are not possible and explain why.
$(a) n = 0, l = 0, m_l = 0, m_s = +1/2$
$(b) n = 1, l = 0, m_l = 0, m_s = -1/2$
$(c) n = 1, l = 1, m_l = 0, m_s = +1/2$
$(d) n = 2, l = 1, m_l = 0, m_s = -1/2$
$(e) n = 3, l = 3, m_l = 3, m_s = +1/2$
$(f) n = 3, l = 1, m_l = 0, m_s = +1/2$

The maximum number of orbitals present in $n=4$ energy level of an atom and the maximum number of electrons with spin value $+\frac{1}{2}$ in the same orbitals are,respectively.

How many unpaired electrons will be present in the ground state of an atom which has valence electronic configuration $3d^6$ in its $+3$ oxidation state?

What is the difference between the ground state and the excited state of a hydrogen atom?