The four distinct points $(0,0), (2,0), (0,-2)$ and $(k,-2)$ are concyclic,if $k$ is equal to

The standard e.m.f. of a cell,involving one electron change is found to be $0.591 \ V$ at $25 \ ^oC$. The equilibrium constant of the reaction is ($F = 96,500 \ C \ mol^{-1}$; $R = 8.314 \ JK^{-1} \ mol^{-1}$)

If $a, b, c$ are three non-coplanar vectors,then the vector equation $r = (1 - p - q)a + pb + qc$ represents a

The diagram shows a force-extension graph for a rubber band. Consider the following statements:
$(I)$ It will be easier to compress this rubber than expand it.
$(II)$ Rubber does not return to its original length after it is stretched.
$(III)$ The rubber band will get heated if it is stretched and released.
Which of these can be deduced from the graph?

If $(x, y, z)$ is an arbitrary point lying on a plane $P$ which passes through the points $(42, 0, 0)$,$(0, 42, 0)$,and $(0, 0, 42)$,then the value of the expression $3 + \frac{x-11}{(y-19)^2(z-12)^2} + \frac{y-19}{(x-11)^2(z-12)^2} + \frac{z-12}{(x-11)^2(y-19)^2} - \frac{x+y+z}{14(x-11)(y-19)(z-12)}$ is:

Nitrobenzene gives $N$-phenylhydroxylamine by