Raita can be frozen but it is not a good practice. Freezing breaks down the protein in the yoghurt which releases water and separates the milk solids. When you thaw frozen raita, it will tend to be watery and thinner in consistency than when you made it fresh. If your raita is specially made with chopped veggies, you shouldn't freeze it as the veggies will also freeze and release water as they thaw.