Which of the following are pure substances? Ice, Milk, Iron, Hydrochloric acid, Mercury, Brick and Water.

Hydrochloric acid, mercury, Ice, Iron and Water are pure substances since they are made up of one or more than one atom of its kind. Also they have their fixed formula while in case of milk (mixture of butter, milk and other ingredients) and brick (mixture of clay, sand etc), they are made by mixing ingredients whose ratio is not fixed. Also they do not have fixed chemical formula.