Which of the following quantities is expressed as force per unit area?

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?

$A$ $U$-tube contains water and methylated spirit separated by mercury. The mercury columns in the two arms are initially in level with $10.0 \; cm$ of water in one arm and $12.5 \; cm$ of spirit in the other. If $15.0 \; cm$ of water and spirit each are further poured into the respective arms of the tube,what is the difference in the levels (in $cm$) of mercury in the two arms? (The specific gravity of spirit is $0.8$.)

The figure shows a container filled with a liquid of density $\rho$. Four points $A, B, C$ and $D$ lie on the diametrically opposite points of a circle as shown. Points $A$ and $C$ lie on a vertical line,and points $B$ and $D$ lie on a horizontal line. Which of the following statements is incorrect? (Here,$p_A, p_B, p_C, p_D$ are the absolute pressures at the respective points.)

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

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