Which of the following are photosynthetic bacteria?

During the estimation of oxalic acid against $KMnO_4$,the self-indicator is:

The area (in square units) bounded by the curves $y^2=4x$ and $x^2=4y$ in the plane is

Sulphur on boiling with $NaOH$ solution gives

$A$ thin metallic spherical shell contains a charge $Q$ on it. $A$ point charge $+q$ is placed at the centre of the shell and another charge $q'$ is placed outside it as shown in the figure. All the three charges are positive. The force on the charge at the centre is:

$A$ $p-n$ photodiode is made of a material with a band gap of $2.0\, eV$. The minimum frequency of the radiation that can be absorbed by the material is nearly