Which one of the lanthanoids given below is the most stable in divalent form?

Given below are two statements :

Statement I : [Ni(CN)₄]^2$$-$$ is square planar and diamagnetic complex, with dsp² hybridization for Ni but [Ni(CO)₄] is tetrahedral, paramagnetic and with sp³-hybridication for Ni.

Statement II : [NiCl₄]^2$$-$$ and [Ni(CO)₄] both have same d-electron configuration have same geometry and are paramagnetic.

In light the above statements, choose the correct answer from the options given below :

Which one of the following techniques is not used to spot components of a mixture separated on thin layer chromatographic plate?

Which of the following structure are aromatic in nature?