Alkaline substances, commonly known as bases, are a class of chemical compounds that can accept protons or donate hydroxide ions (OH?) in reactions. In the pH scale, they have a value greater than 7 and exhibit basic properties such as turning red litmus paper blue. Alkalis play a crucial role in various industries including pharmaceuticals, food processing, water treatment, and manufacturing. They are often used for neutralizing acids, adjusting pH levels, cleaning, and acting as catalysts in chemical reactions. Common examples include sodium hydroxide (NaOH) and potassium hydroxide (KOH).