Block Classification
An element has the outer electronic configuration ending in 3d^5 4s^1; to which block of the periodic table does this element belong?
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About This Question
- Subject
- chemistry
- Chapter
- classification of elements and periodicity in properties
- Topic
- block classification
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
d-block
Elements are classified into s, p, d, and f blocks according to the subshell into which the last electron enters and the subshell being progressively filled. The configuration ending in 3d^5 4s^1 corresponds to chromium, where the differentiating electrons occupy the 3d subshell, so the element belongs to the d-block of transition elements. The half-filled 3d^5 and singly occupied 4s arrangement reflects the extra stability of the half-filled d subshell. The s-block is wrong because its elements end in ns^1 or ns^2 with no partly filled d subshell. The p-block involves filling of np orbitals. The f-block involves filling of inner 4f or 5f orbitals. Identifying block from electronic configuration is a basic NCERT classification skill. Carefully relating the data to the governing principle ensures the reasoning remains valid even when the numbers or species in the question are changed. Plausibility check: chromium is a well-known transition metal with variable oxidation states and coloured ions, hallmarks of the d-block, confirming the classification.
This easy difficulty chemistry question is from the chapter classification of elements and periodicity in properties, covering the topic of block classification. It appeared in the 2025 exam.
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