Bases normally

Analyze the question: We need the general property that bases normally show. Let's test each option.

Concept: Litmus is an indicator.

• Acids turn blue litmus red.
• Bases (alkalis) turn red litmus blue.

Bases also feel soapy, taste bitter, and neutralise acids to form salt and water. They are typically metal oxides or hydroxides.

Step-by-step evaluation:

• A. are corrosive: Only strong bases such as NaOH and KOH are corrosive. Weak bases such as Mg(OH)₂ (milk of magnesia) are not, so this is not true of bases normally.
• B. turn litmus paper from blue to red: This is the behaviour of acids, so it is wrong.
• C. turn litmus paper from red to blue: This is correct. It is the standard test for a base or alkali.
• D. are non-metal oxides: Wrong. Non-metal oxides (CO₂, SO₂) are typically acidic. Basic oxides are metal oxides (CaO, Na₂O).

Answer: C.

Tip: Remember "BRB": Bases turn Red litmus Blue. Acids do the reverse: blue litmus to red.