The diagram shows a simple mercury barometer.Which of the following does not cause the height of the mercury column to vary ?

Consider the wall of a dam to be straight with height $H$ and length $L$. It holds a lake of water of height $h (h < H)$ on one side. Let the density of water be $\rho_{ w }$. Denote the torque about the axis along the bottom length of the wall by $\tau_1$. Denote also a similar torque due to the water up to height $h / 2$ and wall length $L / 2$ by $\tau_2$. Then $\tau_1 / \tau_2$ (ignore atmospheric pressure) is

A vertical $U-$ tube of uniform inner cross section contains mercury in both sides of its arms. A glycerin (density = $1.3 g/cm^3$) column of length $10 $ $cm $ is introduced into one of its arms. Oil of density $0.8 gm/cm^3$ is poured into the other arm until the upper surfaces of the oil and glycerin are in the same horizontal level. Find the length of the oil column ........ $cm$. Density of mercury = $13.6 g/cm^3$

Two copper vessels $A$ and $B$ have the same base area but of different shapes. $A$ takes twice the volume of water as that $B$ requires to fill upto a particular common height. Then the correct statement among the following is

What does it mean when a height of a barometer is rising ?

A liquid $X$ of density $3.36\  g/cm^3$ is poured in a $U-$ tube, which contains $Hg$. Another liquid $Y$ is poured in left arm with height $8\  cm$, upper levels of $X$ and $Y$ are same. What is density of $Y$ .......... $g/cc$