1. Tardigrade
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  4. The correct order of decreasing second ionisation enthalpy of Ti(.22.),V(.23.),Cr(.24.) textandMn(.25.) is-

Q. The correct order of decreasing second ionisation enthalpy of $Ti\left(\right.22\left.\right),V\left(\right.23\left.\right),Cr\left(\right.24\left.\right)\text{and}Mn\left(\right.25\left.\right)$ is-

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Solution:

Electronic configuration of the given elements are
$\text{Mn} → 1 \text{s}^{2} 2 \text{s}^{2} 2 \text{p}^{6} 3 \text{s}^{2} 3 \text{p}^{6} 3 \text{d}^{5} 4 \text{s}^{2}$
$\text{Cr} → 1 \text{s}^{2} 2 \text{s}^{2} 2 \text{p}^{6} 3 \text{s}^{2} 3 \text{p}^{6} 3 \text{d}^{5} 4 \text{s}^{1}$
$\text{Ti} → 1 \text{s}^{2} 2 \text{s}^{2} 2 \text{p}^{6} 3 \text{s}^{2} 3 \text{p}^{6} 3 \text{d}^{2} 4 \text{s}^{2}$
$\text{V} → 1 \text{s}^{2} 2 \text{s}^{2} 2 \text{p}^{6} 3 \text{s}^{2} 3 \text{p}^{6} 3 \text{d}^{3} 4 \text{s}^{2}$
In general, ionization potential ( both 1st and 2nd ) increases form left to right across the period due to increase in effective nuclear charge. On this basis, the second IP values should exhibit the trend :
Mn > Cr > V > Ti
But the actual observed order is :
Cr > Mn > V > Ti
Practically, only chromium is exceptional and rest others show the normal trend. This exceptional behaviour of chromium is due to the stable configuration ( 3d5 ) that it achieves after the loss of first electron.

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