The plot of $r^2 \Psi^2$ versus $r$ for $2s$ orbital of hydrogen atom exhibits :-

Identify the elements represented by the following electronic configurations:
$(a)$ $[He] \, 2s^1$
$(b)$ $[Ne] \, 3s^2 \, 3p^3$
$(c)$ $[Ar] \, 4s^2 \, 3d^1$

$1s^2 2s^2 2p^6 3s^2$ is the electronic configuration of the metal

In a multielectron atom,which of the following orbitals described by three quantum numbers will have the same energy in the absence of electric and magnetic fields?
$A: n=1, \ell=0, m_{\ell}=0$
$B: n=2, \ell=0, m_{\ell}=0$
$C: n=2, \ell=1, m_{\ell}=1$
$D: n=3, \ell=2, m_{\ell}=1$
$E: n=3, \ell=2, m_{\ell}=0$
Choose the correct answer from the options given below:

Choose the correct alternatives. The number of unpaired electrons in an atom of:

The electronic configuration together with the quantum numbers of the last electron for lithium $(Li)$ is: