Rachitha, below is a small animation about some pure substances and impure substances.
This animation initially suggests that Sugar, Water and Lemon Juice are pure substances.
The word Pure in science has a special meaning. Something is pure if it is only one substance, not a mixture of different substances …….so the sugar, water and lemon juice are considered pure. Lemonade is a mixture of these pure substances so it cannot be considered as pure.
However, it could be argued that the juice of a Lemon is not pure. It has a sharp taste which suggests that it is an acid. It does in fact consist of a MIXTURE of three acids so it is not pure.
A. SALT is however pure it only contains a substance called Sodium Chloride.
B. SUGAR is pure if in only contains a substance called Sucrose
C. RAIN WATER is pure if it only contains a substance called H2O.
D. IRON is pure if it only contains Iron atoms. (if you add Carbon to the iron you get a mixture called Steel)
Like the juice of Lemons .. if any of the above (A,B,C or D) contain anything else they will not be pure.