(a) Surface tension of liquids generally decreases with temperature.

(b) The context explicitly states: 'The viscosity of liquids decreases with temperature, while it increases in the case of gases.' As temperature rises, atoms in liquids become more mobile and η falls, while in gases, random motion increases and η increases.

(c) For solids with elastic modulus of rigidity, the shearing force is proportional to shear strain. For fluids, the context states: 'Unlike a solid, here the stress is found experimentally to depend on rate of change of strain or strain rate.' The coefficient of viscosity η is defined as the ratio of shearing stress to the strain rate.

(d) The increase in flow speed at a constriction follows conservation of mass. The continuity equation (A₁v₁ = A₂v₂) shows that when cross-sectional area decreases, velocity must increase to maintain constant mass flow rate. Bernoulli's principle then explains the corresponding pressure changes.

(e) For a model plane in a wind tunnel, turbulence occurs at a greater speed than for an actual plane. Since the model is smaller in size, it requires higher velocity to achieve the same Reynolds number for dynamic similarity.