Which of the following is a $\pi$-acid ligand?

The area (in square units) of the circle which touches the lines $4x + 3y = 15$ and $4x + 3y = 5$ is

$A$ transistor is connected in common emitter $(CE)$ configuration. The collector supply is $8 \ V$ and the voltage drop across a resistor of $800 \ \Omega$ in the collector circuit is $0.5 \ V$. If the current gain factor $\alpha$ is $0.96$,find the base current in $\mu A$.

The correct order of $S-S$ bond length in the following oxyanions is:
$(I)$ $S_2O_4^{2-}$ $(II)$ $S_2O_5^{2-}$ $(III)$ $S_2O_6^{2-}$

If the circle $x^2+y^2+6x-2y+k=0$ bisects the circumference of the circle $x^2+y^2+2x-6y-15=0$,then $k$ is equal to :

Boron in green plants assists in