Which of the following is a correct property of sodium hydroxide (NaOH) as used in laboratory and industry?

Introduction / Context:
Sodium hydroxide, NaOH, also known as caustic soda, is a very important industrial and laboratory chemical. It is widely used in soap making, drain cleaners, chemical manufacturing and as a strong base in titrations. Knowing its physical properties, such as solubility and odor, helps in handling it safely and predicting its behaviour in different solvents. This question asks you to identify a correct property of sodium hydroxide from several statements, some of which are misleading or incorrect.

Given Data / Assumptions:

• Sodium hydroxide is an ionic compound consisting of Na⁺ and OH⁻ ions.
• Water is a polar solvent, while ether and many organic solvents are nonpolar or weakly polar.
• Rotten egg smell is associated with hydrogen sulfide gas, not sodium hydroxide.
• We consider typical laboratory concentrations and conditions.

Concept / Approach:
NaOH is a strong base that readily dissociates into ions in water. Because water is polar, it stabilises these ions and NaOH is highly soluble, producing a strongly basic solution. On the other hand, nonpolar solvents such as ether do not stabilise ions well, so ionic compounds like NaOH are usually insoluble in such solvents. Sodium hydroxide itself is odourless; any smell in solutions is usually due to other substances. The correct approach is to compare these known facts with each option and select the statement that accurately describes NaOH behaviour.

Step-by-Step Solution:
Step 1: Recognise that NaOH dissolves readily in water, forming Na⁺ and OH⁻ ions and giving a strongly alkaline solution with high pH. Step 2: Ionic compounds like NaOH are generally not soluble in nonpolar solvents such as ether, because there is no strong interaction to stabilise the ions. Step 3: Therefore, the statement that NaOH is highly soluble in water but insoluble in ether and other nonpolar solvents is correct. Step 4: The claim that NaOH is only slowly soluble in water and forms a neutral solution is false; it dissolves quickly and creates a basic solution. Step 5: Rotten egg smell is characteristic of hydrogen sulfide gas (H2S), not sodium hydroxide; NaOH itself has no strong characteristic odor. Step 6: The idea that all the statements are correct or that NaOH is completely insoluble in water contradicts well known experimental facts.

Verification / Alternative check:
Laboratory handbooks and safety data sheets state that sodium hydroxide pellets or flakes are readily soluble in water, with dissolution being strongly exothermic. When preparing NaOH solutions, chemists add the solid slowly to water because the heat released can cause splattering. In contrast, NaOH does not dissolve in diethyl ether or other nonpolar solvents and is often used in separations precisely because it stays in the aqueous phase. No reputable source describes NaOH as having a rotten egg smell. These references confirm that high solubility in water and insolubility in nonpolar solvents is the correct property.

Why Other Options Are Wrong:
Option B is wrong because NaOH dissolves quickly, not slowly, and the resulting solution is strongly basic, not neutral. Option C is incorrect because the rotten egg smell comes from hydrogen sulfide, often produced in reactions involving sulfide ions, but NaOH itself does not smell like rotten eggs. Option D claims all statements are true, which cannot be correct since options B and C are false. Option E, saying NaOH is completely insoluble in water, is the opposite of reality. Only option A accurately describes NaOH as highly soluble in water but insoluble in ether and other nonpolar solvents.

Common Pitfalls:
A common misunderstanding is to associate any strong or unpleasant laboratory smell with common reagents like NaOH, even when the odor comes from contaminants or reaction products. Another pitfall is to assume that if a substance is insoluble in one solvent, it must be insoluble in all solvents, which ignores the important like dissolves like principle. Remember that ionic compounds dissolve well in polar solvents like water but poorly in nonpolar solvents, while many organic compounds show the opposite behaviour. For sodium hydroxide, its strong ionic character makes it very water soluble and essentially insoluble in ether.

Final Answer:
A correct property of sodium hydroxide is that It is highly soluble in water but insoluble in ether and other nonpolar solvents, consistent with its ionic nature and strong basicity.