Limewater's basic properties and indicator reactions

Steps:

• Identify limewater as Ca(OH)₂(aq), a weak base with pH > 7.
• Evaluate each option against base characteristics, flame tests, and indicator behaviors.
• Test D: Methyl orange turns yellow in basic solutions (pH > 4.4).
• Confirm D matches while others contradict known chemistry.

Why D is correct:

• Methyl orange indicator is yellow in basic solutions (pH > 4.4), and limewater's Ca(OH)₂ provides OH⁻ ions for basic pH.

Why the others are wrong:

• A: Bases like Ca(OH)₂ have pH above 7, not below.
• B: Blue-green flame test indicates copper ions, absent in Ca(OH)₂.
• C: Ammonia (NH₃) is a base; it does not react with Ca(OH)₂ to form an ammonium salt.

Final answer: D