In mammals,histamine is secreted by .........

In an $NPN$ transistor circuit,the collector current is $10\, mA$. If $90\%$ of the electrons emitted reach the collector,the emitter current $(i_E)$ and base current $(i_B)$ are given by

$A$ drum of radius $R$ and mass $M$ rolls down without slipping along an inclined plane of angle $\theta$. The frictional force

If $T$ is the surface tension of a soap solution,the amount of work done in blowing a soap bubble from a diameter $D$ to $2D$ is (in $\pi D^2T$)

The collector plate in an experiment on the photoelectric effect is kept vertically above the emitter plate. $A$ light source is turned on and a saturation photocurrent is recorded. An electric field is then switched on which has a vertically downward direction.

Which of the following is the weakest reducing agent?