Which one of the following is not a bioindicator of water pollution?

Two point charges $-q$ and $+q$ are located at points $(0, 0, -a)$ and $(0, 0, a)$ respectively. The electric potential at a point $(0, 0, z)$,where $z > a$ is

If an atom has $13$ electrons in the $M$ shell and $1$ electron in the $N$ shell,then the number of unpaired electrons in that atom will be ............

The major product of the following reaction is

Two wires of the same material and length but diameters in the ratio $1:2$ are stretched by the same force. The elastic potential energy per unit volume for the wires,when stretched by the same force,will be in the ratio: (in $:1$)

The orange coloured compound formed when $H_2O_2$ is added to $TiO_2$ solution acidified with conc $H_2SO_4$ is