The stability of a particular oxidation state of a metal in an aqueous solution can be determined by:

When are $d$-block elements considered as transition elements?

The correct option with the order of melting points of the pairs $(Mn, Fe)$, $(Tc, Ru)$ and $(Re, Os)$ is $:$

Cuprous ion is colourless,while cupric ion is coloured because

An element of the $3d-$ transition series shows two oxidation states $x$ and $y$,which differ by two units. Then:

Assertion $(A)$: Transition elements have higher enthalpies of atomization.
Reason $(R)$: Large number of unpaired electrons present in transition elements facilitate strong interatomic interaction and strong bonding between atoms.