Which of the following is used for making optical instruments?

The figure shows three resistor configurations $R_1$, $R_2$, and $R_3$ connected to a $3 \, V$ battery. If the power dissipated by the configurations $R_1$, $R_2$, and $R_3$ is $P_1$, $P_2$, and $P_3$ respectively, then:

Two insulated metallic spheres of $3\,\mu F$ and $5\,\mu F$ capacitances are charged to $300\,V$ and $500\,V$ respectively. The energy loss,when they are connected by a wire is (in $,J$)

If $\int \sin ^{-1}\left(\frac{2 x}{1+x^2}\right) d x=f(x)-\log \left(1+x^2\right)$ then $f(x)$ is equal to

$A$ magnetic needle lying parallel to a magnetic field is turned through $60^{\circ}$. The work done on it is $W$. The torque required to maintain the magnetic needle in the position mentioned above is

What are the substances which mimic the natural chemical messengers?