Which compound has the lowest melting point?

Systematics refers to the

The distance between the parallel lines given by $(x+7y)^2 + 4\sqrt{2}(x+7y) - 42 = 0$ is

If the circle $x^2+y^2+6x-2y+k=0$ bisects the circumference of the circle $x^2+y^2+2x-6y-15=0$,then $k$ is equal to :

$A$ bullet of mass $0.02\, kg$ travelling horizontally with velocity $250\, ms^{-1}$ strikes a block of wood of mass $0.23\, kg$ which rests on a rough horizontal surface. After the impact,the block and bullet move together and come to rest after travelling a distance of $40\, m$. The coefficient of sliding friction of the rough surface is $(g = 9.8\, ms^{-2})$

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