d-block Elements Questions

Out of ${\text{TiF}}_6^{2-}$, ${\text{CoF}}_6^{3-}$, ${\text{Cu}}_2{\text{Cl}}_2$ and ${\text{NiCl}}_4^{2-}$, the colourless species are:

Which of the following pairs has the same size?

Which of the following ions will exhibit colour in aqueous solutions?

Which of the following complex ion is not expected to absorb visible light?

Four successive members of the first series of the transition metals are listed below. For which one of them the standard potential ($E_{M^{2+}/M}^{\circ }$) value has a positive sign?

The catalytic activity of transition metals and their compounds is ascribed mainly to:

Which one of the following does NOT correctly represent the correct order of the property indicated against it?

Which one of the following statements is correct when ${\text{SO}}_2$ is passed through acidified ${\text{K}}_2{\text{Cr}}_2{\text{O}}_7$ solution?