A transition metal 'M' among Sc, Ti, V, Cr, Mn and Fe has the highest second ionisation enthalpy. The spin only magnetic moment value of $\mathrm{M}^{+}$ion is ____ BM (Near integer) (Given atomic number $\mathrm{Sc}: 21, \mathrm{Ti}: 22, \mathrm{~V}: 23, \mathrm{Cr}: 24, \mathrm{Mn}: 25, \mathrm{Fe}: 26$ )

JEE Main · 2024 · 09 Apr 2024 · Shift 2 · d and f Block Elements

A transition metal 'M' among Sc, Ti, V, Cr, Mn and Fe has the highest second ionisation enthalpy. The spin only magnetic moment value of

M^{+}

ion is
____ BM (Near integer)
(Given atomic number

Sc : 21, Ti : 22, V : 23, Cr : 24, Mn : 25, Fe : 26

)

Answer: 6

Among Sc, Ti, V, Cr, Mn, Fe, chromium shows an anomalously high second ionisation enthalpy because removing the second electron from Cr

^{+}

(

[Ar] 3 d^{5}

, a stable half-filled configuration) requires extra energy.

So

M = Cr

, and

Cr^{+} : [Ar] 3 d^{5}

has 5 unpaired electrons.

μ = n (n + 2) = 5 \times 7 = 35 \approx 5.92 BM \approx 6 BM

JEE Main · 2024 · 09 Apr 2024 · Shift 2 · Integer answer