What is $1$ Torr pressure? And what is $1$ bar?

$A$ tank $5 \ m$ high is half-filled with water and then is filled to the top with oil of density $0.85 \ g/cm^3$. The pressure at the bottom of the tank,due to these liquids is ....... $g \ dyne/cm^2$.

Explain why:
$(a)$ The blood pressure in humans is greater at the feet than at the brain.
$(b)$ Atmospheric pressure at a height of about $6 \; km$ decreases to nearly half of its value at sea level,though the height of the atmosphere is more than $100 \; km$.
$(c)$ Hydrostatic pressure is a scalar quantity even though pressure is force divided by area.

The densities of ice and water are $\rho$ and $\sigma$ respectively. What is the change in volume when a mass $M$ of ice melts?

In the figure, chamber $A$ contains a gas, a movable chamber $B$ is placed on top of the gas and it contains $n$ metal balls. The weight of chamber $B$ and the balls is supported by the gas. Chamber $C$ is a vacuum. Let the gas be in equilibrium at pressure $P$. Let $P^{\prime}$ be the pressure if one of the balls is taken away. Find $(P-P^{\prime}) / P$.

If a vessel containing a fluid of density $\rho$ up to height $h$ is accelerated vertically downwards with acceleration $a_0$,then the pressure by the fluid at the bottom of the vessel is given by the equation ........ ($p_0$ denotes the atmospheric pressure and $g$ denotes the acceleration due to gravity).