Option 1 states that roots of potato, radish, and turnip are used as vegetables. This is incorrect as only the radish and turnip roots are used as vegetables. Potato, however, is not a root vegetable; it is a tuber.

Option 2 states that roots of radish, turnip, and yam are used as vegetables, and this is the correct answer. Radish, turnip, and yam all have edible roots that are commonly consumed as vegetables.

Option 3 states that roots of radish and yam are used as vegetables. This is incorrect as turnip also has edible roots and is used as a vegetable.

Option 4 states that roots of potato and turnip are used as vegetables. This is incorrect as mentioned earlier, potato is not a root but a tuber. Therefore, only the turnip roots are used as vegetables.

In conclusion, option 2 is the correct answer as the roots of radish, turnip, and yam are used as vegetables.