Which of the following is not the property of an ideal fluid?

Given below are two statements:
$Statement$ $(I)$: Viscosity of gases is greater than that of liquids.
$Statement$ $(II)$: Surface tension of a liquid decreases due to the presence of insoluble impurities.
In the light of the above statements,choose the most appropriate answer from the options given below:

When an air bubble rises from the bottom of a lake to the surface,its radius is doubled. The atmospheric pressure is equal to that of a column of water of height $H$. The depth of the lake is:

The radius of an air bubble at the bottom of a lake is $r$,and it becomes $2r$ when the air bubble rises to the top surface of the lake. If $P \text{ cm}$ of water is the atmospheric pressure,then the depth of the lake is: (in $P$)

$A$ liquid is kept in a cylindrical vessel which is being rotated about a vertical axis through the centre of the circular base. If the radius of the vessel is $r$ and the angular velocity of rotation is $\omega$,then the difference in the heights of the liquid at the centre of the vessel and the edge is

As shown in the figure, a liquid is at the same level in both arms of a $U$-tube of uniform cross-section when at rest. If the $U$-tube moves with an acceleration '$f$' towards the right, the difference between the liquid heights in the two arms of the $U$-tube will be (acceleration due to gravity $= g$):