States of Matter : Gases & Liquids Test 14

A simple way to form a drop is to allow liquid to flow slowly from the lower end of a vertical tube of small diameter. The surface tension of the liquid causes the liquid to hang from the tube, forming a pendant. When the drop exceeds a certain size it is no longer stable and detaches itself. The falling liquid is also a drop held together by surface tension.

In general, surface tension decreases when temperature increases because cohesive forces decrease with an increase of molecular thermal activity. The influence of the surrounding environment is due to the adhesive action liquid molecules have at the interface.

The magnitude of surface tension of liquid depends on the attractive forces between the molecules. In ethanol and water, we have hydrogen bonding. However water has more effective H-bonding owing to its small size. Hexane has induced dipole-induced dipole force which is a weak force. So the order is 
III

Vapour pressure depends on both molecular interaction and thermal energy within molecular attraction vapour pressure decreases and with increase in thermal energy vapour pressure increases.
Surface tension depends on both molecular interaction and thermal energy with increase in molecular interaction surface tension increases.
Viscosity is also depends on Molecular interaction, with increase in molecular attraction viscosity increases.

Vapor pressure or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature in a closed system. The equilibrium vapor pressure is an indication of a liquid's evaporation rate.

The correct answer is option D
The SI unit of viscosity is the pascal second [Pa s].
The most common unit of viscosity is the dyne second per square centimeter[dyne s/cm2],
Which is given the name poise [P] after the French physiologist Jean Poiseuille
We know that 1 Pa = 1Nm^-2 and 1N = 1kgms^-2
So, from these relations we can get,
1 Pa-s = 1Nm-2s = 1 kgm-2 s-1
Ten poise equal one pascal second [Pa s] making the centipoise [cP] and millipascal second [mPa s] identical.
Hence, 10 poise = 1 kg m^-1 s^-1

Work done = surface tension×Change in area
Surface tension = 73 dyne cm^-1 or 73 x 10^-3 N/m
Area = 0.10 m²
So, work done = 73×10^-3 x 0.10
= 73 x 10^-4 J or 73×10^-4 x 10⁷ erg
= 7.3×10⁴ erg

Viscosity = kg m^-1 s^-1
Surface tension = N m^-1
Surface energy = J m^-2
For latent heat, we have J kg^-1 and not as in p.

Viscosity of liquids decreases as the temperature rises because at high temperature, molecules have high kinetic energy and can overcome the intermolecular forces to slip past one another between the layers.

In water and glycerine, the intermolecular force that exists is  Hydrogen bonding.
In the case of Hexane, Dispersion forces / London forces exists. 
The order of viscosities of these liquids is hexane < water < glycerine.
Hexane has weakest intermolecular forces and glycerine the strongest. ( three OH groups). 
Therefore, hexane has minimum viscosity and glycerine has maximum viscosity.

Liquids try to reduce their surface tension and also the no of molecules at the surface.So statement I is incorrect. 
Statement II is correct. Small liquid drops have spherical shape as they try to reduce their surface tension and their surface area. So for a fixed volume, the sphere has the least surface area. 

Both statements are true and statement IIis the correct explanation of statement I. As temperature is increased, less work is required to extend the surface of a liquid therefore surface tension decreases. The reason behind is that with increase in temperature, molecular motion increases and so intermolecular forces become less effective.