how can we separate  the mixture of flour water sand and  iron particles?

The separation of a mixture of flour, sand, water and iron particles would have to be separated carefully, as both sand particles and flour particles will not dissolve in water. Firstly, iron particles can be separated from the mixture by the use of a magnet. Iron particles will be attracted by the magnet and hence can be easily separated. Now we are left with water, sand and flour. We know that flour particles are lighter than sand particles, and therefore sand particles will settle down more easily in comparison to flour particles. Thus when sand particles settle down, we can quickly decant the water. This will  leave sand particles behind and the water will contain only lighter flour particles. 

Now, this mixture can be evaporated. Water will evaporate, and flour particles would be left behind.