JEE Main 2025 Jan 29 Shift 1, Chemistry Q11: d-Block Elements

JEE Main2025Jan 29, Shift 1Chemistry

The correct option with order of melting points of the pairs (Mn, Fe), (Tc, Ru) and (Re, Os) is :

A
Fe $<$ Mn, Ru $<$ Tc and Re $<$ Os
B
Mn $<$ Fe, Tc $<$ Ru and Re $<$ Os
C
Mn $<$ Fe, Tc $<$ Ru and Os $<$ Re
D
Fe $<$ Mn, Ru $<$ Tc and Os $<$ Re

Solution

Melting points of transition metals correlate with the number of unpaired $d$ electrons participating in metallic bonding. In the 3d series, Mn ( $3 d^{5} 4 s^{2}$ ) has a half-filled configuration with extra-stable, weakly bonded atoms, so $Mn < Fe$ .

The corresponding 4d and 5d members have stronger metallic bonds. Empirically (NCERT): $Tc < Ru$ and $Os < Re$ , the latter being one of the few cases where the maximum shifts to Re.

$∴$ Mn $<$ Fe, Tc $<$ Ru, Os $<$ Re.

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JEE Main 2025 Jan 29 Shift 1, Chemistry Q11: d-Block Elements

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