Q.The transition element used for making calorimeters is :

Mercury's completely filled 5d and 6s subshells leave no unpaired d-electrons to form strong metallic bonds, so its melting point is exceptionally low — it is the only metal that is liquid at room temperature.

Metallic bonding strength in the d-block depends on the number of unpaired (delocalisable) d-electrons available for metallic bonding — more unpaired electrons give stronger interatomic bonds and hence higher melting/boiling points (which is why elements near the middle of a transition series, like W or Os, have very high melting points). Mercury has the electronic configuration $[Xe]4f^{14}5d^{10}6s^2$ — both the d and s subshells are completely filled, so there are no unpaired electrons to contribute to metallic bonding. This makes the metallic bond in mercury exceptionally weak, giving it the lowest melting point of common metals (−38.8°C), so weak that it exists as a liquid at ordinary room temperature. Caesium (a), though a soft alkali metal with a low m …

Copper calorimeters are standard laboratory equipment because copper conducts heat efficiently and rapidly equilibrates temperature with its contents.

Among transition metals, copper has one of the highest thermal conductivities of any common metal, is relatively unreactive under the mild conditions calorimetry experiments use, and is easy to machine into vessels — all of which make it the traditional material for calorimeter cups. Cr, Ni and Zn do not share this combination …