Question

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The increasing order of the first ionization enthalpies is: 3d series < 4d series <5d series
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Answer 1

Explanation:

When we move downward in a particular group the atomic number is increased, consequently nuclear charge is also increased. Due to this reason 5d-elements have higher nuclear change than 3d and 4d elements, therefore, the outer electrons are attracted strongly by the nucleus in 5d elements. On the other hand, the shielding effect of 4f electrons is very poor due to lanthanide contraction in 5d elements, which further increases from 5d elements than 3s and 4d electrons, where no 4f electrons and lanthanide contraction is present.