StemCET Logo

Chemistry Question 59 – JEE-MAIN 2025

← Back
The number of valence electrons present in the metal among Cr, Co, Fe and Ni which has the lowest enthalpy of atomisation is

The enthalpy of atomisation in transition metals is related to the strength of metallic bonding, which depends on the number of unpaired electrons.

Step 1: Identify the Element with Lowest Enthalpy of Atomisation✦ Active

The enthalpy of atomisation for 3d transition metals generally increases from left to right in the series, reaching a maximum around the middle (e.g., Cr, Mn), and then decreases. This trend is due to the increasing number of unpaired d-electrons contributing to stronger metallic bonding up to a certain point. Among the given elements (Cr, Co, Fe, Ni), Chromium (Cr) is the earliest element in the 3d series. Therefore, Cr has the lowest enthalpy of atomisation among these four elements.

Step 2: Determine Electronic Configuration of Chromium (Cr)○ Expand

The atomic number of Chromium (Cr) is 24. Its electronic configuration is anomalous due to the stability of half-filled d-orbitals.

Cr (Z=24): [Ar]3d54s1
💡 Teacher's Secret Hint

Remember the anomalous electronic configurations for Cr and Cu due to half-filled and fully-filled d-orbitals, respectively.

Step 3: Count the Number of Valence Electrons○ Expand

Valence electrons in transition metals include electrons in the outermost s-orbital and the partially filled d-orbitals. For Cr, the valence electrons are from the 3d and 4s subshells.

Number of valence electrons=5(from 3d)+1(from 4s)=6
✦ STEM Console utilizes AI models to generate step-by-step explanations and math clues. AI can make mistakes.