On her vacations,Veena visits four cities ($A, B, C$,and $D$) in a random order. What is the probability that she visits $A$ before $B$?

The truth table for the following logic circuit is

From a uniform wire,two circular loops are made: $(i)$ $P$ of radius $r$ and $(ii)$ $Q$ of radius $nr$. If the moment of inertia of $Q$ about an axis passing through its centre and perpendicular to its plane is $8$ times that of $P$ about a similar axis,the value of $n$ is (diameter of the wire is very much smaller than $r$ or $nr$).

$A$ point moves in the $xy$-plane such that the sum of its distances from two mutually perpendicular lines is always equal to $5$ units. The area (in sq units) enclosed by the locus of the point is

If $lx^2+3xy-2y^2-5x+5y+k=0$ represents a pair of perpendicular lines,then

Which substance is in higher concentration in blood than in glomerular filtrate?