Transition elements exhibit variable valencies because they release electrons from the following orbits:

The correct set of ions (aqueous solution) with the same colour from the following is:

Which of the following types of metals form the most effective catalysts?

Which of the following has the maximum number of unpaired $d-$ electrons?

Explain the variations in atomic radii of transition elements along the period. The following table provides data for the first transition series:

Element	Sc	Ti	$V$	Cr	Mn	Fe	Co	Ni	Cu	Zn
Metallic Radius $M$ (pm)	$164$	$147$	$135$	$129$	$137$	$126$	$125$	$125$	$128$	$137$

Given below are two statements:
Statement $I$: $Cr^{2+}$ is oxidising and $Mn^{3+}$ is reducing in nature.
Statement $II$: $Sc^{3+}$ compounds are repelled by the applied magnetic field.
In the light of the above statements,choose the most appropriate answer from the options given below: