Total number of isomers possible for the complex $[Co(en)_2Cl_2]$ is

Which compound has a magnetic moment equal to $4.90 \ B.M.$?

Calculate the magnetic moment of a divalent ion in aqueous solution if its atomic number is $25$. (in $BM$)

Identify the ion (hydrated in solution) which is not correctly matched with its spin only magnetic moment (in $BM$) given in brackets.

Which of the following does not show optical isomerism?

Which among the following elements in their respective oxidation states develops the lowest spin-only magnetic moment? (Atomic numbers: $Cu=29, Fe=26, Ni=28, Co=27$)