Which of the following is a micronutrient for plants?

$A$ torch bulb rated as $4.5\, W, 1.5\, V$ is connected as shown in the figure. The $e.m.f.$ of the cell needed to make the bulb glow at full intensity is ............. $V$.

If the distance between the foci of an ellipse is $6$ and the length of the minor axis is $8$,then the eccentricity is

Which of the following species has no $p\pi - p\pi$ bond but has a bond order equal to that of $O_2$?

On the basis of the following $E^o$ values,the strongest oxidizing agent is:
$[Fe(CN)_6]^{4-} \rightarrow [Fe(CN)_6]^{3-} + e^-$; $E^o = -0.35 \ V$
$Fe^{2+} \rightarrow Fe^{3+} + e^-$; $E^o = -0.77 \ V$

If a hydrogen electrode is dipped in a solution of $pH = 3$ and $pH = 6$ and a salt bridge is connected,then the $emf$ of the resulting cell is ........... $V$.