Of the following pairs of species,which one will have the same electronic configuration for both members?

If in nature there may not be an element for which the principal quantum number $n > 4,$ then the total possible number of elements will be

From which source are a continuous emission spectrum and a line absorption spectrum simultaneously obtained?

The ionisation energy of an electron in the ground state of a helium atom is $24.6 eV$. The energy required to remove both electrons is: (in $eV$)

Given below are two statements:
Statement $I$: Atoms are electrically neutral as they contain equal number of positive and negative charges.
Statement $II$: Atoms of each element are stable and emit their characteristic spectrum.
In the light of the above statements,choose the most appropriate answer from the options given below.

An electron passing through a potential difference of $4.9 \ V$ collides with a mercury atom and transfers it to the first excited state. What is the wavelength of a photon corresponding to the transition of the mercury atom to its normal state in $\mathring{A}$?