Import Question JSON

$\text{HINT: Filling of 3d orbital starts from 4-period elements.}$ $\text{Explanation:}$ $\text{The filling of 3d orbital starts from 4 periods onwards. The third period}$ $\text{doesn't contain any element which has 3d electrons. Hence, the answer is}$ $\text{option third.}$ $\text{To understand this better:}$ $\text{The third period elements are: Na (11) to Ar (18).}$ $\text{According to the Aufbau principle, electrons fill orbitals in order of increasing energy:}$ $\text{1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, ...}$ $\text{For third period elements, the electron configuration ends with 3s and 3p orbitals.}$ $\text{The 3d orbital is higher in energy than 4s, so it only starts filling from the fourth}$ $\text{period (starting with Scandium, Sc).}$ $\text{Therefore, no third period element has any electrons in 3d orbitals, let alone}$ $\text{more than one electron in a 3d orbital.}$