The ratio of circumferential stress to longitudinal stress in a thin cylinder subjected to internal hydrostatic pressure can be determined using the principles of mechanics of materials.

When a thin cylinder is subjected to internal hydrostatic pressure, it experiences two types of stresses: circumferential stress and longitudinal stress.

- **Circumferential Stress:** This stress acts tangentially to the cross-section of the cylinder and is perpendicular to the longitudinal axis of the cylinder. It is denoted by σc.
- **Longitudinal Stress:** This stress acts parallel to the longitudinal axis of the cylinder and is perpendicular to the cross-section of the cylinder. It is denoted by σl.

The circumferential stress (σc) can be calculated using the formula:

σc = pd/2t

Where:
p = internal pressure
d = diameter of the cylinder
t = thickness of the cylinder

The longitudinal stress (σl) can be calculated using the formula:

σl = pd/4t

Now, to find the ratio of circumferential stress to longitudinal stress, we can divide the circumferential stress by the longitudinal stress:

σc/σl = (pd/2t)/(pd/4t)

Simplifying the expression, we get:

σc/σl = 2/1

Therefore, the ratio of circumferential stress to longitudinal stress in a thin cylinder subjected to internal hydrostatic pressure is 2:1 or simply 2 (option C).

This means that the circumferential stress is twice the longitudinal stress. It implies that the circumferential stress is greater than the longitudinal stress in a thin cylinder subjected to internal hydrostatic pressure.

(pd/2t)/(pd/4t)=2