Which of the following is the most effective in causing the coagulation of a ferric hydroxide sol?

Who is known as the father of Indian Bryology?

$A$ lead bullet at $27\,^{\circ}C$ just melts when stopped by an obstacle. Assuming that $25\%$ of the heat is absorbed by the obstacle,the velocity of the bullet at the time of striking is ........ $m/s$. (Melting point of lead $= 327\,^{\circ}C$,specific heat of lead $= 0.03\,cal/g\,^{\circ}C$,latent heat of fusion of lead $= 6\,cal/g$,and $J = 4.2\,J/cal$)

$A$ plane $x$ passes through the point $(1, 1, 1)$. If $b, c, a$ are the direction ratios of a normal to the plane, where $a, b, c$ $(a < b < c)$ are the factors of $2001$, then the equation of the plane is

Graphite is a soft solid lubricant and is extremely difficult to melt. What is the reason for this behavior of graphite?

Four particles,each of mass $M$,are placed at the corners of a square of side $L$. The radius of gyration of the system about an axis perpendicular to the square and passing through its centre is: