What is the effect of temperature on:
(i) density            
(ii) surface tension
(iii) viscosity            
(iv) the vapour pressure of a liquid?

(i) Density:  The density of a liquid generally decreases with the increase in temperature because liquids expand on heating i.e. volume increases and therefore, 

(ii) Surface tension. The surface tension of a liquid decreases with the increase in temperature because with the rise in temperature, the kinetic energy of the molecules increases and therefore, intermolecular attraction decreases.
(iii) Viscosity: The viscosity of a liquid decreases with the increase in temperature because with the rise in temperature, the average kinetic energy of the molecules increases which can overcome the intermolecular forces.
(iv) Vapour pressure: Vapour pressure of a liquid increases with the increase in temperature because with the rise in the temperature, the average kinetic energy of the liquid molecules increases. Thus, the number of energetic molecules capable of escaping into the vapour state also increases. As a result, the number of molecules present in the vapour state at equilibrium will also be more. Consequently, the vapour pressure will naturally be greater.