Sequence for pure sodium nitrate via titration and crystallization Steps:

• Start with sodium hydroxide in flask (step 4).
• Titrate to determine acid volume needed (step 1).
• Repeat neutralization without indicator for purity (step 7).
• Evaporate solution to concentrate salt (step 2).
• Cool solution and filter to isolate crystals (step 5).
• Use known NaOH volume for precise stoichiometry (step 6).

Why D is correct:

• It follows the neutralization reaction NaOH + HNO₃ → NaNO₃ + H₂O, using titration for exact molar ratio to avoid impurities, then crystallization for pure solid.

Why the others are wrong:

• A starts with titration before adding base, violating procedure order.
• B adds indicator then repeats without it immediately, skipping base addition.
• C adds indicator after titration and evaporates after cooling, inverting key steps.

Final answer: D