Surface Chemistry

Step 1: Write the dissociation reaction of phosphorus pentachloride:
Step 2: Count the number of gaseous molecules on each side:
Step 3: According to Le Chatelier’s principle, increasing volume (or decreasing pressure) favors the side with more number of gaseous molecules.
Step 4: Since dissociation produces more gas molecules, a larger volume will favor greater dissociation.
Step 5: Therefore, the extent of dissociation of PCl will be more in the 10 L vessel.

Step 1: Freundlich adsorption isotherm is given by: where and are constants and .
Step 2: At low pressure, adsorption is directly proportional to pressure: This corresponds to option (B).
Step 3: At moderate pressure, adsorption follows: This corresponds to option (C).
Step 4: At high pressure, the surface becomes saturated and adsorption becomes independent of pressure: This corresponds to option (A).
Step 5: Hence, all the given relations are valid but in different pressure ranges.

Step 1: Spherical shape of liquid drops Due to surface tension, a liquid tries to minimize its surface area. For a given volume, a sphere has the minimum surface area, hence liquid drops tend to become spherical.
Step 2: Downward movement of water in soils Surface tension along with adhesion between water molecules and soil particles causes capillary action, which plays a role in the movement of water through soil pores.
Step 3: Fall of liquid in a capillary tube In a capillary tube, surface tension and cohesive forces cause the liquid to rise or fall depending on the nature of the liquid and the tube material.
Step 4: Since all the given phenomena are consequences of surface tension, the correct answer is All of these.

Step 1: Analyse Assertion (A). A colloidal solution as a whole is electrically neutral. Although the colloidal particles carry a charge, this charge is balanced by an equal and opposite charge of counter-ions in the dispersion medium.
Step 2: Analyse Reason (R). Colloidal particles usually carry the same type of charge, due to which:
they repel each other,
aggregation is prevented,
the colloidal solution remains stable.
Step 3: Check whether (R) explains (A). Reason (R) explains the stability of colloids, not their electrical neutrality. Electrical neutrality is due to the presence of counter-ions, not due to repulsion between similarly charged particles.
Hence, the correct answer is

Step 1: Identify the most suitable reagent for converting alcohols to alkyl chlorides. Among the given reagents, (thionyl chloride) in presence of pyridine is considered the best reagent for this conversion. Step 2: Reason for using thionyl chloride. The reaction proceeds as: The by-products and are gases and escape from the reaction mixture, driving the reaction to completion. Step 3: Role of pyridine. Pyridine:

Acts as a base to absorb HCl,
Prevents side reactions,
Increases the yield of alkyl chloride.
Step 4: Comparison with other reagents.

PCl and PCl produce solid or liquid by-products, making purification difficult.
Dry HCl with ZnCl (Lucas reagent) is less effective and mainly used for classification of alcohols.
Thus, the best method is using in presence of pyridine.