Which one of the following elements is not an essential micronutrient for plant growth?

If $\frac{x-4}{x^2-5x+6}$ can be expanded in the ascending powers of $x$,then the coefficient of $x^3$ is

$X$-rays of wavelength $0.140 \ nm$ are scattered from a block of carbon. What will be the wavelength of $X$-rays scattered at $90^{\circ}$ (in $nm$)?

The equation $\frac{1}{r} = \frac{1}{8} + \frac{3}{8} \cos \theta$ represents

Considering ideal gas behavior, the expansion work done $(in kJ )$ when $144 g$ of water is electrolyzed completely under constant pressure at $300 K$ is $...$ .
Use: Universal gas constant $( R )=8.3 J K ^{-1} mol^{-1}$; Atomic mass $($in amu$)$: $H =1, O =16$

The perimeter of a sector is a constant. If its area is to be maximum,the sectorial angle is: