when u combined the lemon juice in sugar is still lemon juice but the lemon juice will be sweet or sour When u add sugar it will be sweet lemon juice and if u not add a sugar is still lemon juice but is it sour .
Lemon juice does have acid in it. If you are taking about the lemon juice directly from the fruit, then of course. Even if it is in a juice, lemonade for example, it is still an acid. Lemon juice does not HAVE acid in it, but it IS an acid.