(a) 1s, 2s and 3s - orbitals in Mg-atom are not degenerate because these have different values of n.
(b) 2p_x, 2p_y and 2p_z - orbitals in C-atom are degenerate because these belong to same subshell.
(c) 3s, 3p_x and 3d - orbitals in H - atom are degenerate because for H-atom, the subshells having same value of n have same energies.

Electronic configuration of iron suggests that it contains unpaired electrons\({ 26 }^{ fe }=[Ar{ ] }^{ 18 }{ 3d }^{ 6 }{ 4s }^{ 2 }\)

and hence it is perpendicular whereas has no unpaired electron
\({ 26 }^{ fe }=[Ar{ ] }^{ 18 }{ 3d }^{ 6 }{ 4s }^{ 2 }\)and hence, it is diamagnetic. it is rather repelled by the magnet.

\({ NH }_{ 4 }^{ + }\) ion contains covalent and dative bonds. (It is formed by donation of lone pair of electrons on N in NH₃ to H⁺ ion). \({ NO }_{ 3 }^{ - }\) ion also contains covalent and davite bonds.
Bond between \({ NH }_{ 4 }^{ + }\) and \({ NO }_{ 3 }^{ - }\) ions is ionis.
N of \({ NH }_{ 4 }^{ + }\) ion is sp³ hydridised and is tetrahedral.
N of \({ NO }_{ 3 }^{ - }\) ion is sp² hybridised and is planar.

 Density, d = pM/RT
For same gas at different temperatures and pressures
\(\cfrac { { d }_{ 2 } }{ d_{ 1 } } =\cfrac { { p }_{ 2 }{ T }_{ 1 } }{ { p }_{ 1 }{ T }_{ 2 } }\)
\( { d }_{ 2 }=\cfrac { { p }_{ 2 }{ T }_{ 1 }d_{ 1 } }{ { p }_{ 1 }{ T }_{ 2 } } \)
\(\cfrac { 1\times 300\times 5.46 }{ 2\times 273 } \)
= 3 g dm^-3

Consider two molecules to be spherical, if r is the radius of the molecules then the distance of closest approach between the two molecules = 2r (as shown in Figure). This is the distance between the centres of their nuclei.

Since the molecules cannot come closer than distance 2r, the excluded volume for a pair of molecules = volume of sphere of radius 2r
\(=\frac { 4 }{ 3 } \pi { \left( 2r \right) }^{ 3 }=8\times \frac { 4 }{ 3 } \pi { r }^{ 3 }\) 
\(\therefore \) Excluded volume per molecules (b)
\(=\frac { 1 }{ 2 } \left( 8\times \frac { 4 }{ 3 } \pi { r }^{ 3 } \right) =4\times \frac { 4 }{ 3 } \pi { r }^{ 3 }\)  
But \(\frac { 4 }{ 3 } \pi { r }^{ 3 }={ V }_{ m }\), i.e. the actual volume of the gas molecule.
\(\therefore \)  b = 4V_m

\({ CaCO }_{ 3 }(s)\rightleftharpoons CaO(s)+{ CO }_{ 2 }(g)\) 
K_p = \({ p }_{ { CO }_{ 2 } }\) = 1.15 atm, pV = nRT
\({ N }_{ { CO }_{ 2 } }=\frac { { P }_{ { CO }_{ 2 } } }{ RT } =\frac { 1.15\times 5 }{ 0.082\times 1073 } =0.065mol\) 
1 mole of CO₂ is obtained by decomposition of 1 mole CaCO₃. Therefore, moles of CaCO₃ decomposed is equal to the moles of CO₂ = 0.065 mol.
Moles of CaCO₃ initially present = \(\frac { 50 }{ 100 } =0.5 \ mol\) 
[Molecular mass of CaCO₃ = 100]
Percent of CaCO₃ decomposed  \(=\frac { 0.065 }{ 0.5 } \times 100=13\)%

Due to this property hydrogen is used for the manufacture of vanaspati ghee from edible oils such as cotton-seed oil, soyabean oil, corn oil etc.
\(unsaturated \ oil \ + \ H_{ 2 }(g)\overset { Ni \ catalyst }{ \longrightarrow } Vanaspati\quad ghee\)

Producer gas is a mixture of CO and N₂, therefore, the tetravalent element is carbon and its monoxide and dioxide are CO and CO₂ respectively.
\(2C(s)+\underbrace { O_{ 2 }(s)+4N_{ 2 }(g) }_{ Air } \overset { 1273k }{ \rightarrow } \underbrace { 2CO(g)+4N_{ 2 }(g) }_{ Producer \ gas } \)
The carbon monoxide is a strong reducing agent and reduces ferric oxide to iron.
\(Fe_{ 2 }O_{ 3 }(s)+3CO(g)\overset { \Delta }{ \rightarrow } 2Fe(s)+3CO_{ 2 }(g)\)

The general formula of alkanes is C_nH_2n+2=12xn+1x(2n+2)=72 or 12n+2n+2=72 or n=5
Thus, the molecular formula of the alkane is C₅H₁₂. For structural isomers and their IUPAC names.