Chemistry S & P Block Elements MDCAT 2019
PMDC Verified Question 79 of 104
Oxidation number of particular element can be directly or indirectly inferred from its:
A
Physical state
B
Group number
C
Atomic size
D
Atomic mass
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Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Group number
Concept:

The oxidation number indicates the total number of electrons an atom either gains or loses to form a chemical bond. This behavior is directly tied to its valence electrons.

Solution:

  • The periodic table is structured such that an element's Group number (in the A-group classification, e.g., IA, IIA, VIIA) corresponds directly to the number of valence electrons in its outermost shell.
  • For example, Group IA metals have 1 valence electron, so they exhibit a +1 oxidation state. Group VIIA (Halogens) have 7 valence electrons, needing 1 to complete the octet, so their most common state is -1.
  • Therefore, the group number provides a direct roadmap to an element's oxidation states.


Why other options are incorrect:

  • Options A, C, & D: Physical state (solid/liquid/gas), size, and mass do not dictate electron exchange chemistry and cannot reliably predict oxidation states.

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