Which cell organelle can be identified by Sudan Black?

$A$ metal wire $PQ$ slides on parallel metallic rails having a separation of $0.25\ m$,each having negligible resistance. There is a $2\,\Omega$ resistor and a $10\ V$ battery as shown in the figure. $A$ uniform magnetic field of magnitude $0.5\ T$ is directed into the plane of the paper. $A$ force of $0.5\ N$ to the left is required to keep the wire $PQ$ moving with a constant speed to the right. With what speed is the wire $PQ$ moving? (Neglect self-inductance of the loop)

For the $RC$ circuit shown,the resistance is $R = 10.0 \ \Omega$,the capacitance is $C = 5.0 \ \mu F$ and the battery has voltage $\xi = 12 \ V$. The capacitor is initially uncharged when the switch $S$ is closed at time $t = 0$. At some time later,the current in the circuit is $0.50 \ A$. What is the magnitude of the charge across the capacitor at that moment in $\mu C$?

The number of common tangents to the circles $x^2+y^2-4x-6y-12=0$ and $x^2+y^2+6x+18y+26=0$ is

Which of the following is not an example of a natural polymer?

The number of solutions $(x, y, z)$ to the system of equations $x+2y+4z=9$,$4yz+2xz+xy=13$,$xyz=3$,such that at least two of $x, y, z$ are integers is