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)

$$ \text { Match the following. } $$

$$ \begin{array}{cccc} \hline & \begin{array}{c} \text { List-I } \\ \text { (Atomic number) } \end{array} & & \begin{array}{c} \text { List-II } \\ \text { (Group number and } \\ \text { period number) } \end{array} \\ \hline \text { A. } & 56 & \text { I. } & 9,4 \\ \hline \text { B. } & 50 & \text { II. } & 3,6 \\ \hline \text { C. } & 27 & \text { III. } & 14,5 \\ \hline \text { D. } & 58 & \text { IV. } & 2,6 \\ \hline \end{array} $$

The correct answer is

According to molecular orbital theory, the molecule which contains only $\pi$-bonds between the atoms is