On bisecting a soap bubble along a diameter, the force due to surface tension on any of its half part will be

The correct option is 4πRT.

Step-by-Step Explanation:
1. Understanding the Soap Bubble Structure: A soap bubble is composed of a thin liquid film. Because it is hollow and contains air inside, it has two free surfaces in contact with air: an inner surface and an outer surface.
2. Analyzing the Bisection: When the soap bubble of radius $R$ is bisected along its diameter, the cross-section is a circle of radius $R$.
3. Determining the Effective Length: The force of surface tension acts along the boundary line of the cut. Since there are two concentric surfaces (inner and outer), each with a circular boundary of circumference $2\pi R$, the total effective length $L$ over which surface tension acts is twice the circumference:

$L=2\times \left(2\pi R\right)=4\pi R$

4. Calculating the Force: The force $F$ due to surface tension $T$ is defined as the product of the surface tension and the total contact length along which it acts:

$F=T\times L$

Substituting the value of the effective length $L$ into the equation:

$F=T\times 4\pi R=4\pi RT$

Thus, the force due to surface tension on any of the half parts of the bisected bubble is $4\pi RT$.