Which of the following naturally contains oxalic acid?

The correct answer is Spinach.

Key Points

• Spinach is known to naturally contain high levels of oxalic acid.
• Oxalic acid in spinach can bind with minerals to form oxalates, which may affect mineral absorption.
• Spinach is also rich in vitamins, especially vitamin K, A, and C.
• It is widely consumed in various dishes, including salads, soups, and smoothies.

Additional Information

• Apples: Apples are a good source of dietary fiber and vitamin C. 
• Milk: Milk is a rich source of calcium, protein, and vitamin D. 
• Vinegar: Vinegar is an acidic liquid produced from the fermentation of ethanol. It primarily contains acetic acid.