Among the following elements, which one has the lowest melting point at standard atmospheric pressure?

Introduction / Context:
Understanding melting point trends helps learners distinguish between metals, non metals and noble gases. Metals and many non metallic solids have relatively high melting points compared to light noble gases, which exist as monatomic gases at room temperature. This question compares the melting points of titanium, sulphur, argon and zinc to identify which element has the lowest melting point, reinforcing the idea that noble gases condense only at very low temperatures.

Given Data / Assumptions:
- Titanium and zinc are metallic elements that are solid at room temperature.
- Sulphur is a non metallic solid under normal conditions.
- Argon is a noble gas that exists as isolated atoms in the gaseous state at room temperature.
- Standard atmospheric pressure is assumed for comparison of melting points.

Concept / Approach:
Metals have strong metallic bonding which requires significant energy to break, so they tend to have high melting points. Sulphur forms molecular crystals made of S8 rings and has a moderate melting point but still melts above room temperature. Noble gases like argon are held together in the solid state only by very weak dispersion forces and therefore condense and freeze at temperatures close to absolute zero. Consequently, argon has a much lower melting point than titanium, sulphur or zinc and will be the correct answer in any such comparison.

Step-by-Step Solution:
Step 1: Identify that titanium and zinc are metals with strong metallic bonds, leading to high melting points. Step 2: Note that sulphur is a non metal that exists as S8 molecules in the solid state and melts at a moderate temperature above room temperature. Step 3: Recognise that argon is a noble gas present as individual atoms in the gas phase under normal conditions. Step 4: Recall that noble gases like argon only solidify at very low temperatures because the forces between their atoms are extremely weak. Step 5: Conclude that argon has the lowest melting point among the elements listed.

Verification / Alternative check:
Approximate numerical values support this reasoning. Titanium and zinc both have melting points in the hundreds or even more than one thousand degrees Celsius, characteristic of metals. Sulphur melts slightly above one hundred degrees Celsius. In contrast, argon has a melting point far below zero degrees Celsius on the Celsius scale, reaching the solid state only under cryogenic conditions. Even if the exact temperatures are not memorised, knowing that argon is a noble gas while the others are solids at room temperature clearly indicates that argon melts at the lowest temperature.

Why Other Options Are Wrong:
Titanium is a high melting metal used in aerospace and structural applications and clearly does not have a low melting point. Zinc, though lower melting than some metals, still melts at several hundred degrees Celsius and is used as a coating metal, not a cryogenic solid. Sulphur melts above room temperature and is used in matches and sulphuric acid manufacture, but it is still a solid in ordinary conditions. Magnesium, another metal included as a distractor, also has a relatively high melting point compared with argon. None of these candidates can compete with a noble gas in terms of having the lowest melting point.

Common Pitfalls:
Students may be tempted to think of sulphur as having a low melting point because it is a non metal and can melt in a laboratory test tube with modest heating. However, they may forget that argon is not a solid at all under normal conditions and reaches the solid state only at extremely low temperatures. Another pitfall is to focus only on metals and compare them among themselves, ignoring the non metallic option. Remembering that noble gases condense last when cooled helps to correctly identify argon as the element with the lowest melting point here.

Final Answer:
Among the given elements, the one with the lowest melting point is Argon.