The number of hydroxide ions produced by one molecule of sodium carbonate $(Na_2CO_3)$ on hydrolysis is

Gold numbers of protective colloids $A$,$B$,$C$ and $D$ are $0.50$,$0.01$,$0.10$ and $0.005$,respectively. The correct order of their protective powers is

Who among the following is known as the 'Father of Taxonomy'?

If $x_1$ and $x_2$ are the real roots of the equation $x^2-kx+c=0$,then the distance between the points $A(x_1, 0)$ and $B(x_2, 0)$ is

If $l, m, n$ are in arithmetic progression,then the straight line $lx + my + n = 0$ will always pass through the point:

The value of $k$ such that the lines $2x - 3y + k = 0$,$3x - 4y - 13 = 0$,and $8x - 11y - 33 = 0$ are concurrent,is