Answer:

The dynamic viscosity of a fluid is a measure of its resistance to flow under an applied force. It is defined as the ratio of the tangential force per unit area to the velocity gradient perpendicular to the direction of flow. The unit of dynamic viscosity is called the poise (P).

The poise is defined as the force required to move a surface of 1 square centimeter at a speed of 1 centimeter per second, with a shear stress of 1 dyne per square centimeter.

Now let's analyze the options given:

a) dyne/cm2: This unit is for shear stress, not dynamic viscosity. It represents the force per unit area required to cause deformation in a material.

b) dyne-s/cm2: This is the correct unit for dynamic viscosity. It represents the force per unit area required to maintain a velocity gradient of 1 cm/s perpendicular to the flow direction.

c) gm-s/cm2: This unit represents the dynamic viscosity in terms of grams, which is incorrect. The unit should be in dyne-s/cm2, not gm-s/cm2.

d) gm-cm/s: This unit represents the kinematic viscosity, which is the ratio of dynamic viscosity to density. It is not the same as dynamic viscosity.

Therefore, the correct answer is option 'B', dyne-s/cm2.

To summarize, the poise is the unit of dynamic viscosity, and it is equivalent to dyne-s/cm2. It represents the force required to maintain a velocity gradient of 1 cm/s perpendicular to the flow direction.