C

Step 1: Understanding surface tension: Surface tension is defined as the force acting per unit length along the surface of a liquid.
Step 2: The formula for surface tension (A) can be denoted as:
$$\gamma = \frac{F}{L}$$
where $\gamma$ is the surface tension, $F$ is the force acting on the surface, and $L$ is the length along which the force acts.
Step 3: SI units: The SI unit of force is Newton (N), and the SI unit of length is meter (m). Therefore, surface tension is measured in Newtons per meter (N/m).
Step 4: Evaluating options:
- Option A (Dyne/cm) is not the SI unit.
- Option B (Newton/cm) is incorrect since the unit of length should be in meters.
- Option C (Newton/metre) correctly represents the SI unit of surface tension.
- Option D (Newton-metre) is a measure of torque, not surface tension.
Conclusion: Hence, the correct answer is Option C: Newton/metre.