Correct statement regarding the dichromate ion (Cr₂O₇^2–) is:

1. 4 Cr-O bond lengths are equal.

2. 6 Cr-O bond lengths are equal.

3. All Cr-O bond lengths are equal.

4. None of the Cr-O bond lengths are equal.

Electronic configuration of a transition element X in +3 Oxidation state is [Ar]3d⁵. What is its atomic number?

1. 25

2. 26

3. 27

4. 24

Gadolinium belongs to 4f series. It's atomic number is 64. Which of the following is the correct electronic configuration of gadolinium?

(a) [Xe]4f⁸6d²                    (b) [Xe]4f⁹5s¹

(c) [Xe]4f⁷5d¹6s²                   (d) [Xe]4f⁶5d²6s²

Reason of lanthanoid contraction is

(1) negligible screening effect of 'f orbitals

(2) increasing nuclear charge

(3) decreasing nuclear charge

(4) decreasing screening effect

Which of the following ions will exhibit colour in aqueous solutions ?
(a) La³⁺ (Z=57)
(b) Ti³⁺ (Z=22)
(c) Lu³⁺ (Z=71)
(d) Sc³⁺ (Z=21)

A pair among the following that has both coloured ions in the aqueous solution is-
(At. no : Sc =21, Ti = 22, Ni = 28, Cu = 29, Co = 27)

Which of the following is called Wilkinson's catalyst?

(1) $\left[\mathrm{RhCl}\right({\mathrm{PPh}}_3{)}_3]$             (2) ${\mathrm{TiCl}}_4+({\mathrm{C}}_2{\mathrm{H}}_5{)}_3\mathrm{Al}$

(3) $({\mathrm{C}}_2{\mathrm{H}}_5{)}_4\mathrm{Pb}$                  (4) $\left[{\mathrm{PtCl}}_2\right({\mathrm{NH}}_3{)}_2]$

Which of the following solid salt on heating with solid ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ and  conc.${\mathrm{H}}_2{\mathrm{SO}}_4$ orange red vapours are evolved which turn aqueous NaOH solution yellow?

(a)NaBr               (b) NaCl

(c) ${\mathrm{NaNO}}_3$           (d) NaI

Which of the following is true for the species $3{\mathrm{d}}^4$ configuration ?

(A) ${\mathrm{Cr}}^{2+}$ is reducing in nature                               

(B) ${\mathrm{Mn}}^{3+}$ is oxidising in nature.

(C) Both (A) and (B)                                             

(D) None of these

In which compound does vanadium have an oxidation number of +4?

(1) ${\mathrm{NH}}_4{\mathrm{VO}}_2$                                 

(2) ${\mathrm{K}}_4\left[\mathrm{V}{\left(\mathrm{CN}\right)}_6\right]$

(3) ${\mathrm{VSO}}_4$                                     

(4) ${\mathrm{VOSO}}_4$