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

Introduction / Context:
Melting point is a basic physical property that helps compare the thermal stability of elements and compounds. Metals generally have high melting points due to strong metallic bonding, whereas light gases condense and freeze at very low temperatures. This question asks which element among chromium, hydrogen, zinc and silver has the lowest melting point, encouraging students to recall that hydrogen is a light diatomic gas that becomes solid only at extremely low temperatures.

Given Data / Assumptions:
- Chromium, zinc, silver and copper are typical metals under normal conditions.
- Hydrogen at room temperature is a diatomic gas (H2), not a metal.
- Melting point refers to the temperature at which a solid becomes a liquid at one atmosphere pressure.
- We compare only the relative order of melting points, not exact numerical values.

Concept / Approach:
Metals such as chromium, zinc, silver and copper have strong metallic bonding and closely packed crystal lattices, which require significant energy to break, resulting in high melting points. In contrast, hydrogen molecules interact only through weak intermolecular forces when in condensed phases. Hydrogen becomes liquid and solid at cryogenic temperatures far below zero degrees Celsius. Therefore hydrogen has a much lower melting point than the given metallic elements, which already exist as solids at everyday temperatures.

Step-by-Step Solution:
Step 1: Identify the physical state of each element at room temperature. Chromium, zinc, silver and copper are solid metals, whereas hydrogen is a gas. Step 2: Recall that metals typically possess high melting points due to strong metallic bonds and ordered crystal structures. Step 3: Recognise that hydrogen needs extremely low temperatures to solidify, so its melting point is far below that of most metals. Step 4: Understand that chromium, zinc and silver all have melting points hundreds of degrees Celsius above room temperature. Step 5: Conclude that hydrogen has the lowest melting point among the listed elements.

Verification / Alternative check:
Approximate data confirm this reasoning. The melting points of most structural metals such as chromium and copper are well above one thousand degrees Celsius, while zinc and silver still melt at several hundred to around one thousand degrees Celsius. Hydrogen, by comparison, transitions from solid to liquid at temperatures close to absolute zero on the Kelvin scale. Even without remembering the exact numbers, the fact that hydrogen is a light gas under normal conditions while the others are high melting solids confirms the qualitative comparison.

Why Other Options Are Wrong:
Chromium, zinc and silver all have much higher melting points than hydrogen. They are solids at room temperature and require strong heating to melt. Copper, an additional metal included as a distractor, also has a high melting point and does not compete with hydrogen in this respect. None of these metallic elements can have a lower melting point than a light diatomic gas like hydrogen.

Common Pitfalls:
Students sometimes confuse boiling point and melting point, or they may guess based on which metal they think is softer or more easily deformed. Softer metals do not necessarily have the lowest melting point in a group. Another pitfall is to overlook the stark difference between gases and metals and to focus only on the metals listed. Remembering that gases condense and freeze only at very low temperatures helps quickly identify hydrogen as the element with the lowest melting point in this set.

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