The maximum number of unpaired electrons that can be present in $d$-orbitals is

Explain the Aufbau principle with an example.

Nickel atom can lose two electrons to form $Ni^{2+}$ ion. The atomic number of nickel is $28$. From which orbital will nickel lose two electrons?

$4d, 5p, 5f$ and $6p$ orbitals are arranged in the order of decreasing energy. The correct option is

The orbital angular momentum of a $3p$ electron is

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: