Which of the following ions are diamagnetic ?

German silver is an alloy of $Cu$ with

Which of the following statements are correct?

$(A)$ The electronic configuration of $Cr$ is $[ Ar ] 3 d ^{5}$ $4 s^{1}$.

$(B)$ The magnetic quantum number may have a negative value.

$(C)$ In the ground state of an atom, the orbitals are filled in order of their increasing energies.

$(D)$ The total number of nodes are given by $n-2$.

Choose the most appropriate answer from the options given below ....

If the colours of salts of transition elements are due to the presence of unpaired electrons in the transition metal ions, which of the following ions will be colourless in aqueous solution

On adding excess of $N{H_3}$ solution to $CuS{O_4}$ solution, the dark blue colour is due to

$(a)$ Transition metals can act as catalysts because these can change their oxidation state. How does $Fe(III)$ catalyse the reaction between iodide and persulphate ions ?

$(b)$ Mention any three processes where transition metals act as catalysts.