The minimum value of $|z-1|+|z-5|$ is

Three concentric metallic spherical shells of radii $R, 2R, 3R$ are given charges $Q_1, Q_2, Q_3$ respectively. It is found that the surface charge densities on the outer surfaces of the shells are equal. Then,the ratio of the charges given to the shells,$Q_1 : Q_2 : Q_3$ is

Explain the hydrostatic paradox.

$A$ pendulum is oscillating with frequency $n$ on the surface of the earth. It is taken to a depth $d = \frac{R}{2}$ below the surface of the earth. What is the new frequency of oscillation at this depth? [$R$ is the radius of the earth]

Coordination compounds have great importance in biological systems. In this context,which of the following statements is incorrect?

The locus of the centre of a circle which passes through the origin and cuts off a chord of length $4$ units from the line $x=3$ is