The correct statement(s) regarding the binary transition metal carbonyl compounds is(are) (Atomic numbers : $$Fe = 26,Ni = 28$$)

A reversible cyclic process for an ideal gas is shown below. Here, $$P, V,$$ and $$T$$ are pressure, volume and temperature, respectively. The thermodynamic parameters $$q,w, H$$ and $$U$$ are heat, work, enthalpy and internal energy, respectively.



The correct option(s) is (are)

The compounds(s) which generate(s) $${N_2}$$ gas upon thermal decomposition below $${300^ \circ }C$$ is (are)

Consider an ionic solid $$MX$$ with $$NaCl$$ structure. Construct a new structure $$(Z)$$ whose unit cell is constructed from the unit cell of $$MX$$ following the sequential instructions given below. Neglect the charge balance.
$$(i)\,\,\,\,\,$$ Remove all the anions $$(X)$$ except the central one

$$(ii)\,\,\,\,$$ Replace all the face centered cations $$(M)$$ by anions $$(X)$$

$$(iii)\,\,$$ Remove all the corner cations $$(M)$$

$$(iv)\,\,\,\,$$ Replace the central anion $$(X)$$ with cation $$(M)$$

The value of $$\,\,\left( {{{number\,\,of\,\,anions} \over {number\,\,of\,\,cations}}} \right)\,\,$$ in $$Z$$ is ___________.