Consider a mercury-filled tube as shown in the figure below. Which of the following options about the pressures at the lettered locations $(A, B, C, D)$ is true?

Define pressure. Give the $SI$ and $CGS$ unit of pressure.

It is difficult to heal a wound on a mountain. Why? Explain.

$A$ spherical marble of radius $1 \, cm$ is stuck in a circular hole of radius slightly smaller than its own radius (for calculation purpose,both can be taken same) at the bottom of a bucket filled with water up to a height of $10 \, cm$. If the mass of the marble is $20 \, g$,then the net force on the marble due to water is close to:

$A$ siphon in use is demonstrated in the following figure. The density of the liquid flowing in the siphon is $1.5 \text{ g/cm}^3$. The pressure difference between the points $P$ and $S$ will be

$A$ cubical block of wood, of length $10 \,cm$, floats at the interface between oil of density $800 \,kg/m^3$ and water. The lower surface of the block is $1.5 \,cm$ below the interface. If the depth of water is $10 \,cm$ below the interface and oil is up to $10 \,cm$ above the interface, then the difference in pressure at the lower and the upper face of the wooden block is:
(Assume density of water, $\rho_w = 1000 \,kg/m^3$ and acceleration due to gravity, $g = 10 \,m/s^2$) (in $\,Pa$)