Give reasons for the following: Paramagnetic character in the first transition series increases upto manganese and then decreases.

In the 3d transition series as we move from Scandium to manganese, the number unpaired electrons increases and hence paramagnetic character increases. After Manganese, the pairing of electrons in the d-orbital starts and the number of unpaired electrons decreases and hence, paramagnetic character decreases.

Give reasons for the following: Transition elements exhibits catalytic property.

Transition metal and their compounds exhibit catalytic properties due to the following reasons: (i). Due to their variable oxidation state, they form an intermediate complex, thereby providing a new path for reaction. (ii). Availability of empty d-orbital which provides good surface area for reaction.

Give reasons for the following: There is a steady decrease in atomic or ionic radii of lanthanides from lanthanum to lutetium.

Lanthanide contraction is the steady decrease in the size of the ions and atoms of the rare earth elements with increasing atomic numbers from lanthanum to lutetium. For every consecutive atom, the nuclear charge can be more positive by a single unit, accompanied by the corresponding increase in the electron count present in the 4 f orbitals surrounding the nucleus. These electrons imperfectly protect each other from the increased positive charge of the nucleus, resulting in a steady rise in the effective nuclear charge attracting every electron as the lanthanide elements progress, resulting in successive decreases in ionic and atomic radii.

Lu + H 2 O → X + H 2 ; Identify X .

Lanthanoids react with water to liberate hydrogen. The reaction occurs slowly with cold water but rapidly with hot water. Lutetium reacts with water to form lutetium trihydroxide and hydrogen. 2 Lu + 6 H 2 O → 2 Lu ( OH ) 3 + 3 H 2

Transition elements forms alloys. Write the reason.

Transition elements form intermetallic alloys because they have atoms of nearly the same size. Their atoms can mutually substitute each other in the metal lattice. They also form interstitial alloys like stainless steel, chrome steel etc.

Name any two elements of the d block which are not considered as transition elements.

A transition metal may be defined as the one that has an incomplete inner d - orbital. A transition metal is also called a transition element. In the case of transition elements, electrons are added successively to the inner d - orbitals. These elements are called transition elements as they are placed between s - and p - block elements and their properties represent a transition between the highly reactive electropositive elements of the s -block and the electronegative elements of the p - block. The elements Zn , Cd and Hg remain at the end of 3 d , 4 d and 5 d series respectively whose atoms have completely filled d -orbitals for which they are non-transitional.

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If ${KMnO}_{4}$ is reduced by oxalic acid in acidic medium, then the oxidation number of $Mn$ changes from _____ .

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