Chlorine has two isotopes $\text{Cl}^{37}$ and $\text{Cl}^{35}$ with percentage abundance of $25\%$ and $75\%$ respectively. Find average atomic mass of chlorine ?

Calculate the shortest wavelength in hydrogen spectrum emission of Lymen series ($R_H = 109677\,\text{cm}^{-1}$)

What is the number of bond pair of electrons and lone pair of electrons present in the valence shell of chalcogens in their hydride ?

Which of the following is favourable condition for the formation of ionic bond ?