The correct answer is option 1. Cr.
Chromium (Cr) has a half-filled 3d subshell with five unpaired electrons, leading to strong metallic bonds and the highest melting point among the given options (1857°C).
The melting point of an element is a measure of the temperature at which it transitions from a solid to a liquid state. Among the elements of the 3d transition metal series (scandium to zinc), chromium (Cr) has the highest melting point. Let's explore this in more detail:
1. Electronic Configuration:
Chromium has the electronic configuration \([Ar] 3d^5 4s^1\). The partially filled 3d orbitals contribute to its unique electronic structure.
2. Effect of Electron Configuration on Melting Point:
The electronic configuration of an element can influence its physical and chemical properties. Chromium exhibits exceptional stability due to its half-filled 3d orbital, resulting in a relatively high melting point.
3. Explanation of Chromium's High Melting Point:
Chromium has a high melting point compared to its neighboring elements in the 3d series. The half-filled 3d subshell provides increased stability, which contributes to the strength of metallic bonding. The stability of the half-filled 3d subshell is associated with the exchange energy, also known as the "exchange stabilization."
4. Comparison with Other Elements:
Manganese (Mn), iron (Fe), and cobalt (Co) are neighboring elements to chromium in the 3d series. While they also have high melting points, chromium surpasses them due to the stability associated with its electronic configuration.
5. Melting Points of 3d Series Elements:
Chromium (Cr): ~1,857°C
Manganese (Mn): ~1,246°C
Iron (Fe): ~1,538°C
Cobalt (Co): ~1,495°C
6. Industrial Applications:
Chromium's high melting point is advantageous in applications that require materials with excellent heat resistance.
Chromium is commonly used in the production of high-temperature alloys and stainless steel.
In summary, chromium's high melting point can be attributed to its unique electronic configuration, specifically the half-filled 3d subshell, which enhances the stability of the element and contributes to the strength of metallic bonding. This characteristic makes chromium a valuable element in various industrial applications where high-temperature stability is crucial. | 
