If the amplitude of $z - 2 - 3i$ is $\pi / 4$,then the locus of $z = x + iy$ is

If $a, b, c, d$ are positive real numbers such that $\frac{a}{3} = \frac{a+b}{4} = \frac{a+b+c}{5} = \frac{a+b+c+d}{6}$,then the value of $\frac{a}{b+2c+3d}$ is

Which of the following acids has the lowest $pK_a$ value?

What is obtained from yeast?

Cattle fed with spoilt hay of sweet clover which contains dicumarol:

$A$ wire of length $l$ is bent into a circular loop of radius $R$ and carries a current $I$. The magnetic field at the centre of the loop is $B$. The same wire is now bent into a double loop of equal radii. If both loops carry the same current $I$ and it is in the same direction,the magnetic field at the centre of the double loop will be