81.

Which one of the following pairs of elements is called 'chemical twins' because of their very similar chemical properties ?

• Mn and W

• Mo and Tc

• Fe and Re

• Hf and Zr

Effective magnetic rnoment of Sc³⁺ ion is :

• 1.73

• 0

• 5.92

• 2.83

Potassium permanganate acts as an oxidant in alkaline and acidic media. The final products formed from KMnO₄ in the two conditions are respectively

• MnO^2- and Mn³⁺

• Mn³⁺ and Mn²⁺

• Mn²⁺ and Mn³⁺

• MnO₂ and Mn²⁺

The catalytic activity of the transition metals and their compounds is described to :

• their chemical reactivity 

• their magnetic behaviour

• their unfilled d-orbitals

• their ability to adopt multiple oxidation states and their complexing ability

The magnetic moment µ, of transition metals is related to the number of unpaired electrons, n as:

• μ = $\sqrt{\mathrm{n} \left(\mathrm{n} + 2\right)}$

• μ = n (n + 2)²

• μ = n² (n + 2)

• μ = n/ (n + 2)

The compound ZnFe₂O₄ is:

• a normal spinel compound

• a inverse spinel compound

• interstitial compound

• covalent compound

Ferrous ion charges to X ion, on reacting with acidified hydrogen peroxide. The number of d-electrons present in X and its magnetic moment (in BM) are, respectively :

• 6 and 6.93

• 5 and 5.92

• 5 and 4.9

• 4 and 5.92

A complex compound of Co³⁺ with molecular formula CoCl_x. yNH, gives a total of 3 ions when dissolved in water. How many Cl^- ions satisfy both primary and secondary valencies is this complex?

• 3

• 1

• 4

• zero

Identify the correct order in which the covalent radius of the following elements increases

                    (I)Ti, (II) Ca, (III) Sc

• (I), (II), (III)

• (III), (II), (I)

• (II), (I), (III)

• (I), (III), (I)

Which of the following pair of transition metal ions, have the same calculated values of magnetic moment ?

• Ti²⁺ and V²⁺

• Fe²⁺ and Cu²⁺

• Cr²⁺ and Fe²⁺

• Co²⁺ and Ti²⁺