Which microorganism is used for the commercial production of citric acid?

If the charge on a body is increased by $2 \ C$,the energy stored in it increases by $21 \%$. The original charge on the body in coulomb is

In which of the following reactions is $H_2O_2$ acting as a reducing agent?

Sodium and copper have work functions of $2.3 \ eV$ and $4.5 \ eV$ respectively. The ratio of their threshold wavelengths is nearest to:

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

Consider the following statements $A$ and $B$ and identify the correct answer.
$A$. In an elastic collision,if a body suffers a head-on collision with another of the same mass at rest,then the first body comes to rest while the other starts moving with the velocity of the first one.
$B$. Two bodies of equal mass suffering a head-on elastic collision merely exchange their velocities.