Identify a molecule which does not exist.

Which of the following is the most electronegative element?

Which of the following are paramagnetic? A. $\left[\mathrm{NiCl}_4\right]^{2-}$ B. $\mathrm{Ni}(\mathrm{CO})_4$ C. $\left[\mathrm{Ni}(\mathrm{CN})_4\right]^{2-}$ D. $\left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$ E. $\mathrm{Ni}\left(\mathrm{PPh}_3\right)_4$ Choose the correct answer from the options given below :

Given below are two statements : Statement I : Ferromagnetism is considered as an extreme form of paramagnetism. Statement II : The number of unpaired electrons in a $\mathrm{Cr}^{2+}$ ion $(\mathrm{Z}=24)$ is the same as that of a $\mathrm{Nd}^{3+}$ ion $(Z=60)$. In the light of the above statements, choose the correct answer from the options given below :

Which of the following statements are true? A. Unlike Ga that has a very high melting point, Cs has a very low melting point. B. On Pauling scale, the electronegativity values of N and Cl are not the same. C. $\mathrm{Ar}, \mathrm{K}^{+}, \mathrm{Cl}^{-}, \mathrm{Ca}^{2+}$, and $\mathrm{S}^{2-}$ are all isoelectronic species. D. The correct order of the first ionization enthalpies of $\mathrm{Na}, \mathrm{Mg}, \mathrm{Al}$, and Si is $\mathrm{Si}\gt\mathrm{Al}\gt\mathrm{Mg}\gt\mathrm{Na}$. E. The atomic radius of Cs is greater than that of Li and Rb . Choose the correct answer from the options given below

Given below are two statements: Statement I : Like nitrogen that can form ammonia, arsenic can form arsine. Statement II : Antimony cannot form antimony pentoxide. In the light of the above statements, choose the most appropriate answer from the options given below: