Viscosity is a fundamental property of fluids that describes their resistance to flow. It is commonly measured in units of Pascal-seconds (Pa·s) or poise (P). However, the options provided in the question are not in the standard units of viscosity. Let's analyze each option to determine the correct answer.

a) metres^2 per sec:
This unit does not represent viscosity. The square metres (m^2) in the numerator and seconds (s) in the denominator suggest an area-to-time ratio, which is not related to viscosity.

b) kg sec/metre^2:
This unit represents dynamic viscosity, also known as absolute viscosity, expressed in kg/(m·s). It is the force required to move one layer of fluid relative to another, divided by the area and time. While this unit is related to viscosity, it is not the standard unit.

c) newton-sec per metre^2:
This unit represents dynamic viscosity in the standard SI unit of Pascal-seconds (Pa·s). The newton (N) is the SI unit of force, and dividing it by the area in square metres (m^2) and time in seconds (s) gives us the correct unit for viscosity.

d) newton-sec^2 per metre:
This unit does not represent viscosity. The second power of newton-seconds (N·s^2) in the numerator and metres (m) in the denominator do not correspond to any physical property related to viscosity.

Therefore, the correct answer is option 'C': newton-sec per metre^2. This unit represents the dynamic viscosity of a fluid in the standard SI unit of Pascal-seconds (Pa·s).