Iron fillings are added to water, and sink to the bottom. is this a mixture or a solution ?

It is a Mixture

A mixture is a combination of different things that are not chemically bonded.

A solution is a special type of homogeneous mixture composed of two or more substances. A solute is a substance dissolved in another substance, known as a solvent and when this happens a solution is formed

answer: the rate of diffusion increases with increase in temperature.

increase in temperature, increases the molecular/particles speed (kinetic energy. diffusion means movement of particles through the material.

generally, the heavier the particle the more it interacts with the environment and more the temperature matters. so higher temperature results in higher diffusion.

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.