The ratio of the difference in energy between the first and second Bohr orbits to that between the second and third orbit is

In the reaction I and II the covalencies of Be and Al in $X$ and $Y$ are respectively

I. $\mathrm{Be}(\mathrm{OH})_2+\underset{\text { (Excess) }}{\mathrm{NaOH}} \longrightarrow X$

II. $\mathrm{Al}(\mathrm{OH})_3+\underset{\text { (Excess) }}{\mathrm{NaOH}} \longrightarrow Y$

The energy of second orbit of hydrogen atom is $-5.45 \times 10^{-19} \mathrm{~J}$. What is the energy of first orbit of $\mathrm{Li}^{2+}$ ions (in J)?

The number of electrons with $(n+l)$ values equal to 3,4 and 5 in an element with atomic number $(Z) 24$ are respectively

( $n=$ principal quantum number and $l=$ azimuthal quantum number)