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Classification of Elements and Periodicity in Properties

Multiple Choice Questions

141.

Among the following groupings which represent the collection of isoelectronic species.

NO⁺, C $_{2}^{2 -}$ , C $_{2}^{-}$ , CO
N₂, C $_{2}^{2 -}$ , CO, NO
CO, NO⁺, CN^-, C $_{2}^{2 -}$
NO, CN^-, N₂, O $_{2}^{-}$

142.

Which element has maximum first ionisation potential?

143.
Atomic radii of which metals are same?

Cr, Mn, Cu

Cr, Fe, Co

Sc, Ti, Zn

V, N, Cr

Cr, Mn, Cu

The atomic radii of elements from Cr to Cu (i.e. Cr, Mn, Cu) are very close to one another. This is due to ffective screening of outer ns-electrons by the electrons of (n -1) d subshell.

The reason for the anomalous increase in atomic radii towards the end of the series is predominant repulsion between the added electrons. Presence of completely flled d-orbitals also decreases the force of attraction.