The synthesis of crotonaldehyde from acetaldehyde is an example of $.......$ reaction.

The colour of $KMnO_4$ is due to

$A$ straight line $L$ at a distance of $4$ units from the origin makes positive intercepts on the coordinate axes,and the perpendicular drawn from the origin to this line makes an angle of $60^{\circ}$ with the line $x+y=0$. Then the equation of the line $L$ is

If the pair of straight lines given by $A x^2+2 H x y+B y^2=0$ $(H^2>A B)$ forms an equilateral triangle with the line $a x+b y+c=0$,then $(A+3 B)(3 A+B)$ is equal to :

$A$ magnetic needle is kept in a non-uniform magnetic field. It experiences

Which of the following organs is known as the 'blood bank' of the human body?