The above diagram shows the arrangement for observing the scattering of light in the colloidal solution. Why does the beaker appear orangish-red when it is seen through the slit MN?
Because blue light scatters the most and the remaining colours pass nearly unscattered.
As bluish set of colours have shorter wavelengths, they get scattered the most and remaining colors pass nearly unscattered. Hence the colors which pass unscattered will constitute a color which is without blue i.e. it will appear as orangish-red.