The system with the largest internal pressure is

Correct option is C

​A soap bubble has two liquid surfaces which are in contact with air, one inside the soap bubble and the other outside the soap bubble. At equilibrium conditions, the air pressure inside the soap bubble is increased than the outside pressure, and the extra pressure is called excess pressure.

Due to the surface tension force, the small bubbles and liquid drops are spherical. The pressure inside a liquid drop or a bubble is greater than the pressure outside it.

Excess pressure inside a liquid drop

Let the radius of a liquid drop be R. let the surface tension of the liquid be T. Let p1 be the pressure inside the liquid drop. Let p2 be the pressure inside the liquid drop. The different kinds of forces that act on the liquid drop are:

a) The force is caused due to surface tension. Ft=2πRT(towards the right)

​b) The force is caused due to outside pressure.F1=P1πR²(towards the right)

c) The force is caused due to inside pressure.F2=P2πR²(towards left)

The drop is in the state of equilibrium, so Ft=  F2– F1

2πRT = P2πR²– P1πR²

=>(P2– P1) πR²= 2πRT

=> excess pressure = P2– P1= 2T/R 

Excess pressure inside a soap bubble

Let the radius of a soap bubble be R. Let the soap bubble’s surface tension be T. Let p1 be the pressure inside the soap bubble. Let p2 be the pressure inside the soap bubble. 

A soap bubble consists of two liquid surfaces in contact with the air. So, the total force on the surface of the soap bubble that is caused due to surface tension will be 2×2πRT. The different kinds of forces that act on the soap bubble are:

a) A force that is caused due to surface tension. Ft=4πRT (towards the right)

b) The force is caused due to outside pressure.F1=P1πR²(towards the right)

c) The force is caused due to inside pressure.F2=P2πR²(towards left) 

The drop is in the state of equilibrium, so Ft=  F2– F1

4πRT = P2πR²– P1πR²

=>(P2– P1) πR²= 4πRT

=> excess pressure = P2– P1= 4T/R 

Pure water has a relatively high surface tension compared to solutions with dissolved ions or surfactants.

Soap solution reduces the surface tension significantly due to the surfactant, which results in a lower internal pressure.

NaCl solution (sodium chloride) dissociates into Na+ and Cl− ions. The presence of these ions in the solution affects the surface tension and typically results in a moderate decrease in surface tension compared to pure water but less than soap.

Sugar solution is molecular and does not significantly alter the surface tension compared to water, but it does not reduce it as much as NaCl or soap solutions.​