Based on Heisenberg's uncertainty principle, the uncertainty in the velocity of the electron to be found within an atomic nucleus of diameter $$10^{-15} \mathrm{~m}$$ is ________ $$\times 10^9 \mathrm{~ms}^{-1}$$ (nearest integer)

[Given : mass of electron $$=9.1 \times 10^{-31} \mathrm{~kg}$$, Plank's constant $$(h)=6.626 \times 10^{-34} \mathrm{Js}$$] (Value of $$\pi=3.14$$)

In the given TLC, the distance of spot A & B are 5 cm & 7 cm, from the bottom of TLC plate, respectively.

$$\mathrm{R}_{\mathrm{f}}$$ value of $$\mathrm{B}$$ is $$x \times 10^{-1}$$ times more than $$\mathrm{A}$$. The value of $$x$$ is __________.

Number of compounds from the following which cannot undergo Friedel-Crafts reactions is: _________

toluene, nitrobenzene, xylene, cumene, aniline, chlorobenzene, $$m$$-nitroaniline, $$m$$-dinitrobenzene

Total number of electrons present in $$\left(\pi^*\right)$$ molecular orbitals of $$\mathrm{O}_2, \mathrm{O}_2^{+}$$ and $$\mathrm{O}_2^{-}$$ is ________.